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1 EARLY PALEOGENE CROCODYLIFORM EVOLUTION IN THE NEOTROPICS: EVIDENCE FROM NORTHEASTERN COLOMBIA By ALEXANDER K. HASTINGS A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT O F THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2012
2 2012 Alexander K. Hastings
3 To my father, mother and fiance
4 ACKNOWLEDGMENTS I thank my committee for all their contributions throughout my research. This dissertation would not have been possible without their instruction and guidance. I must in particular acknowl edge my advisor Jonathan Bloch for his enormous help and assistance with all aspects of my academic career at the University of Florida. E. M artin, D. Foster, M. Brenner, and J. Head have all been terrific and helpful mentors throughout the course of my research at UF Thanks to the UF Department of Geological Sciences, especially J. Jaeger and M. Perfit, for supporting me through this long Ph. D. and giving me the opportunity to become a professional. Several funding sources have aided in varying aspects of the research including: the National Science Foundation Grant DEB 0733725 and DSGC 640179, funds from the Department of Geological Sciences and the Florida Museum of Natural History at the University of Florida, the Smithsonian Tropical Research Institute Paleobiology Fund, the Geological Society of America Graduate Student Research Grant, the R. Jerry Britt, Jr. Paleobiology Award, the Gary S. Morgan Student Research Award, and the Cerrej n Coal mine. Funding was also acquired from the Theodore Roosevelt Research Grant, American Museum of Natural History. Many thanks to L. Teicher, F. Chavez, G. Hernandez, C. Montes, and the rest of the crew at the Cerrej n coal mine for access to the site and housing during field work. Thanks to Ecopetrol S.A. ICP for logistic support. Thanks to H. Garcia, A. Rincon, E. Cadena, F. Herrera, M. Carvalho, S. Wing, M. Ramirez J. Moreno Bernal for help collecting fossils at Cerrej n. Lastly, thanks to the Colombian Geological and Mining Institute (INGEOMINAS) in Bogot Colombia, for access to specimens and facilitating ongoing research of the remarkable vertebrate fossils of the Paleocene of Colombia. I
5 thank the museum curators, collection managers, and registrars who have assisted me with collections at other museums including: D. Brinkman C. Mehling, L. Steel R. Pelligrini, D. Kizirian R. Pascocello Thanks to R. Hulbert and J. Bourque for countless helpful conversations and advice. Thanks to K. Krysko and M. Nickerson for constant access to and assistance with the FLMNH Herpetology collections. Thanks to my fellow museum graduate students A. Rincon, E. Cadena, F. Hererra, P. Morse, E. Woodruff, C. Manz, J. Mathis S. Allen, D. Ehret, L. Grawe Desantis, L. HelenaOviedo, and S. Moran for discussions, feedback, and for being sounding boards for so many failed and successful ideas Thanks to the very helpful staff of the UF Geology Department for keeping things in order throughout my degree. Thanks to my incredibly loving and supporting parents K. and N. Hastings who in all honesty have funded a large portion of this dissertation. Thanks to my fiance, K. Rowe, for helping me through the trying times and support ing me through thick and thin. I would like to thank D. Steadman, J. Krigbaum, and B. MacFadden for their assistance with nondissertation research and for the opportunity to be involved in interesting research from other regions of the world. Thanks also to J. Krigbaum for stepping in at the last minute to make my graduation possible. Last but by no means least, m any thanks to C. Jaramillo for the opportunity to be involved in this region of the world and for pulling together much of the necessary funding and logistics to m ake this dissertation possible.
6 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 9 LIST OF FIGURES ........................................................................................................ 11 ABSTRACT ................................................................................................................... 14 CHAPTER 1 INTRODUCTORY REMARKS ................................................................................ 16 2 A NEW SMALL SHORT SNOUTED DYROSAURID (CROCODYLOMORPHA, MESOEUCROCODYLIA) FROM THE PALEOCENE OF NORTHEASTERN COLOMBIA ............................................................................................................. 22 Introduction ............................................................................................................. 22 Institutional Abbreviations ................................................................................. 24 Terminology and Anatomical Abbreviations ..................................................... 24 Systematic Paleontology ......................................................................................... 25 Cerrejonisuchus G en. N ov. ............................................................................. 25 Cerrejonisuchus improcerus S p. N ov. ............................................................. 25 Preservation ..................................................................................................... 27 Description ....................................................................................................... 27 Comparison ...................................................................................................... 44 Phylogenetic Relationships ..................................................................................... 51 Discussion .............................................................................................................. 54 3 A NEW LONGIROSTRINE DYROSAURID (CROCODYLOMORPHA, MESOEUCROCODYLIA) FROM THE PALEOCENE OF NORTHEASTERN COLOMBIA: BIOGEOGRAPHIC AND BEHAVIOURAL IMPLICATIONS FOR NEW WORLD DYROSAURIDAE ........................................................................... 72 Introduction ............................................................................................................. 72 Institutional A bbrev iations ................................................................................. 74 Terminology and A natomical A bbreviations ..................................................... 75 Systematic Paleontology ......................................................................................... 75 Acherontisuchus G en. N ov. ............................................................................. 75 Acherontisuchus guajiraensis S p. N ov. ........................................................... 75 Description ....................................................................................................... 77 Comparison ...................................................................................................... 83 Phylogenetic Relationships ..................................................................................... 89 Discussion .............................................................................................................. 91 Dispersal .......................................................................................................... 91
7 Paleobiology ..................................................................................................... 96 4 A NEW BLUNT SNOUTED DYROSAURID (CROCODYLOMORPHA, MESOEUCROCODY LIA) FROM THE PALEOCENE OF COLOMBIA ................. 120 Introduction ........................................................................................................... 120 Institutional Abbreviations ............................................................................... 121 Terminology and Anatomical Abbreviations ................................................... 122 Systematic Palaeontology ..................................................................................... 122 Unnamed Taxon, N ew G enus and S pecies .................................................... 122 Description ..................................................................................................... 123 Comparison .................................................................................................... 131 Phylogenetic Analysis ........................................................................................... 139 Relationship to O ther D yrosaurids .................................................................. 139 Relationship of Dyrosauridae to O ther C rocodyliforms ................................... 142 Biogeography ................................................................................................. 144 Discussion ............................................................................................................ 145 5 DYROSAURID MORPHOSPACE AND DIVERSITY THROUGH TIME ................ 168 Introduction ........................................................................................................... 168 Geometric Morphometric Analysis ........................................................................ 172 Materials and M ethods ................................................................................... 172 Results ........................................................................................................... 176 Morphospace Discussion ............................................................................... 179 Diversity Analyses ................................................................................................ 181 Methods .......................................................................................................... 181 Results ........................................................................................................... 184 Diversity Discussion ....................................................................................... 185 6 CONCLUSION ...................................................................................................... 205 Dyrosaurid Systematics ........................................................................................ 205 Phylogeny ............................................................................................................. 205 Biogeography ........................................................................................................ 206 Paleobiology ......................................................................................................... 207 Morphospace and Diversity .................................................................................. 208 Concluding Remarks ............................................................................................. 208 APPENDIX A CLADISTIC ANALYSIS CHARACTER LIST ......................................................... 209 B C HARACTER MATRIX FOR DYROSAURID CLADISTIC ANALYSIS .................. 219 C CHARACTER MATRIX FOR CROCODYLOMORPH CLADISTIC ANALYSIS ..... 223
8 D COMPARISON OF UNNAMED TAXON TO DIAGNOSES OF OTHER DYROSAURIDS ................................................................................................... 226 E MODERN SPECIMENS USED FOR GEOMETRIC MORPHOMETRIC ANALYSIS ............................................................................................................ 228 F DYROSAURID FIGURES USED FOR GEOMETRIC MORPHOMETRIC ANALYSIS ............................................................................................................ 235 LIST OF REFERENCES ............................................................................................. 237 BIOGRAPHICAL SKETCH .......................................................................................... 250
9 LIST OF TABLES Table page 2 1 Snout proportions for Cerrejonisuchus and other members of Dyrosauridae .... 59 2 2 Alveolar measurements of Cerrejonisuchus ...................................................... 60 3 1 Snout proportions for Acherontisuchus and other members of Dyrosauridae 102 4 1 Snout proportions for Unnamed Taxon and other members of Dyrosauridae 150 5 1 Percent variance for individual relative warps in the adult dyrosaurid and crocodylian relative warp analysis ................................................................... 188 5 2 Correlation statistics for ontogenetic study of four extant crocodylian species 190 5 3 Relative disparity values fro m the geometric morphometric study from a total of 219 skulls of crocodylians and dyrosaurids. ................................................. 191 5 4 Diversity values for marine predators from the Late Cretaceous through Eocene. ............................................................................................................ 192 5 5 Pearson correlation statistics for diversity curves.. ........................................... 193 B 1 Character taxon matrix for first 28 characters used in phylog enetic analyses of Dyrosauridae. ............................................................................................... 219 B 2 Character taxon matrix for characters 29 54 used in phylogenetic analyses of Dyrosauridae.. .............................................................................................. 221 B 3 Character taxon matrix for characters 55 82 used in phylogenetic analyses of Dyrosauridae ............................................................................................... 222 C 1 Coded character states for characters 1 30. .................................................... 224 C 2 Coded character states for characters 31 60. .................................................. 224 C 3 Coded character states for characters 61 90. .................................................. 224 C 4 Coded character states for characters 91 120. ................................................ 224 C 5 Coded character states for characters 121 150 ............................................... 224 C 6 Coded charact er states for characters 151 180 ............................................... 224 C 7 Coded character states for characters 181 210 ............................................... 224
10 C 8 Coded character states for charac ters 211 234 ............................................... 225 E 1 Extant crocodylian specimen list arranged by taxon and collection. ................. 229 F 1 Reference images for Dyrosauridae. ................................................................ 236
11 LIST OF FIGURES Figure page 1 1 Paleocene map of all fossil vertebrate localities. ................................................ 21 2 1 World map of locations of known crocodyliform fossil s. ...................................... 61 2 2 Location and stratigraphic column from which fossils of Cerrejonisuchus were recovered. ........................................................................................................... 62 2 3 Skull of Cerrejinosuchus improcerus UF/IGM 29, in dorsal view ...................... 63 2 4 Skull of Cerrejinosuchus improcerus UF/IGM 29, in lateral and occipital views .................................................................................................................. 64 2 5 Skull of Cerrejonisuchus improcerus UF/IGM 29, in ventral view ..................... 65 2 6 Referred skull of Cerrejonisuchus improcerus UF/ IGM 31, in dorsal view ........ 66 2 7 Referred snout of Cerrejonisuchus improcerus UF/IGM 32. .............................. 67 2 8 Referred mandible of Cerrejonisuc hus improcerus UF/IGM 30 ......................... 68 2 9 Results from phylogenetic analysis of 82 characters and 14 taxa ...................... 69 2 10 Phylogenetic relationship placed in stratigraphic and paleobiogeographic context ................................................................................................................ 70 2 11 Associated postcrania of UF/IGM 31 .................................................................. 71 3 1 Geographic and strat igraphic position for the localities of all known fossils of Acherontisuchus guajiraensis ........................................................................... 103 3 2 Acherontisuchus guajiraensis maxillary fragments .. 104 3 3 Acherontisuchus guajiraensis mandible ................... 105 3 4 Referred mandible in dorsal view of Acherontisuchus guajiraensis 35. .................................................................................................................... 106 3 5 Acherontisuchus guajirae nsis ...................................................................................................... 107 3 6 Referred mandible of Acherontisuchus guajiraensis region only. ....................................................................................................... 108 3 7 otype of Acherontisuchus guajiraensis associated teeth and ribs ................................................................................................................... 109
12 3 8 Acherontisuchus guajiraensis ......... 110 3 9 Acherontisuchus guajiraensis ........................................................................... 111 3 10 New World dyrosaurid pelvis fossils ................................................................. 112 3 11 Acherontisuchus guajiraensis ........................ 113 3 12 X .................. 114 3 13 Strict consensus cladograms from phylogenetic analyses of Dyrosauridae. .... 115 3 14 Majorty rule consensus tree of phylogenet ic analysis placed in stratigraphic and palaeobiogeographic context. .................................................................... 116 3 15 Proposed routes for three independent dyrosaurid dispersal events from Africa to the New World .................................................................................... 117 3 16 Reconstruction of skeleton of Acherontisuchus guajiraensis with muscle attachments to pelvic region ............................................................................. 118 3 17 Pitch regulation in a generalized dyrosaurid crocodyliform. .............................. 119 4 1 Locality map and stratigraphic column for locality where all known Unnamed Taxon fossils are found. ................................................................................... 151 4 2 Holotype (UF/IGM 67) of new genus and species of Dyrosauridae ................. 152 4 3 Paratype (UF/IGM 68) of new genus and species of Dyrosauridae ................. 153 4 4 Referred skull (UF/IGM 69) of new genus and species of Dyrosauridae. ......... 154 4 5 Orbital tuberosities of r eferred skull (UF/IGM 69) of new genus and species of Dy rosauridae. ............................................................................................... 155 4 6 Associated articular bone of UF/IGM 68. .......................................................... 156 4 7 Vertebrae associated with skulls of the new genus and species of Dyrosauridae.. .................................................................................................. 157 4 8 Ribs and haemal arch associated with skulls of the new genus and species of Dyrosauridae ................................................................................................ 158 4 9 Por tions of the pelvis of the new genus and species, UF/IGM 68. .................... 159 4 10 Proximal phalanx of the new genus and species, UF/IGM 68 .......................... 160 4 11 Dyrosaurid osteoderms .................................................................................... 161
13 4 12 Cladograms resulting from a phylogenetic analysis of Dyrosauridae ............... 162 4 13 Two cladograms from analyses utilizing a matrix with representatives of all of Crocodylomorpha. ............................................................................................ 163 4 14 Cladogram resulting from biogeographic analysis of Dyrosauridae using the program S DIVA. .............................................................................................. 164 4 15 Map showing dispersal pattern and timing for Dyrosauridae.. .......................... 165 4 16 Bivariate plot of interorbital width of dyrosaurids and extant crocodylians. ...... 166 4 17 Portions of pelomedosoid turtle carapace, UF/IGM 71 with crocodyliform bite marks ............................................................................................................... 167 5 1 Diagrams a nd example used in geometric morphometric study ....................... 194 5 2 Morphospace x y scatter plot of 209 adult crocodylian skulls ........................... 195 5 3 Morphospace x y scatter plot of all 10 dyrosaurid taxa known from reasonably complete skulls. ............................................................................. 196 5 4 Morphospace x y scatter plot of combined dyrosaurid and extant crocodylian morphospace .................................................................................................... 197 5 5 Morphospace x y scatter plot of combined dyrosaurid and extant crocodylian morphospace with clades highlighted. .............................................................. 198 5 6 Correl ation x y scatter plots of fo ur species of extant crocodylia. ..................... 199 5 7 X Y scatter plot of first two relative warps showing morphospace occupation resulting from combining the ontogenetic study set and Dyrosauridae. ............ 200 5 8 Morphospace x y scatter plots for each geologic stage for Dyrosauridae ........ 201 5 9 Results of dispari ty analyses generated from geometric morphometric study of Dyrosauridae through geologic time ............................................................ 202 5 10 Uncorrected generic diversi ty curves of marine predators through geologic time ................................................................................................................... 203 5 11 Residual diversity curves of marine predators .................................................. 204
14 Abstract Of Dissertation Presented To The Graduate School Of The University Of Florida In Pa rtial Fulfillment Of The Requirements For The Degree Of Doctor Of Philosophy EARLY PALEOGENE CROCODYLIFORM EVOLUTION IN THE NEOTROPICS: EVIDENCE FROM NORTHEASTERN COLOMBIA By Alexander K. Hastings August 2012 Chair: Jonathan I. Bloch Major: Geolog y Muc h of the fossil record of northern South America has been poorly sampled largely as a consequence of the dense vegetation throughout the region. Newly acquired f ossil reptiles from the Paleocene (58 60 million years ago) of northeastern Colombia document t he northern South American terrestrial fauna from this time. The crocodyliforms from the Cerrejn Formation of northeastern Colombia indicate three new genera and species of the extinct Dyrosauridae The family was known pr imarily from saltwater/brackishw ater deposits before, but these taxa represent the first adult freshwater forms that can be identified beyond the family level. The three species include a dwarf f or m, Cerrejonisuchus improcerus which is the smallest known dyrosaurid. The second is a more typical dyrosaurid, Acherontisuchus guajiraensis with a longirostrine skull. The third is also a new form for Dyrosauridae, a largebodied, blunt snouted form Results from phylogenetic analys e s of these and other dyrosaurids support three independent di spersal events from Africa to the New World. P ostcrania associated with the new species have morphology indicating differences in lifestyle from other dyrosaurids. The skull shapes of Cerrejonisuchus and the blunt snouted form are different from any other known dyrosaurids Skull shape can be quantified using
15 geometric morphometric methods, but such a study must include another group for meaningful comparison. Given the availability of modern species, a dataset was gathered from 242 extant crocodylian skull s, including all living species and all ten dyrosaurids known from reasonably complete skulls. Dyrosaurid morphospace is more than doubled with the addition of the Cerrejn taxa and the resulting measured disparity for Dyrosauridae exceeds that of all livi ng crocodylia. Four extant species had a significant relationship between dorsal skull length (a proxy for age) and the first relative warp The same shift in morphospace is seen between the Cerrejn dyrosaurids and longirostrine ones, implying a possible connection between retention of juvenile traits and a short snout. There is a significant inverse correlation between dyrosaurid diversity through geologic time (with and without the Cerrejn species) and other marine carnivores .
16 CHAPTER 1 INTRODUCTORY REM ARKS Geology and paleontology of the Paleogene are difficult to study in the tropics because rocks of the appropriate age are very often covered by dense vegetation and flooded basins and the ancient life of northern South America has been largely unknown from before the Miocene. The Cerrejn coal mine in northeastern Colombia is one of the worlds largest openpit coal mines, and has exposed large sections of the Paleoceneaged Cerrejn Formation, from when the world was warmer than today (Head et al., 200 9). The formation contains over 150 economic coal bearing layers that are stripped off for commercial purposes by the corporation Carbones del Cerrejn L t d and was found to be between 58 and 60 million years old (Jaramillo, 2007) Below the coal layers ar e thick underclays that are exposed after each coal bearing layer is removed. These underclays were deposited in a large fluvial environment that likely drained into a lagoon or estuarine habitat during the Paleocene (Jaramillo et al., 2007). The underclay s also contain fossils of plants and animals from this time period living in this ancient ecosystem. The plants from this formation indicate that many of the taxa that make up the modern rainforests of northern South America were present in the early Paleogene, forming the first neotropical rainforests (Doria et al., 2008; Herrera et al., 2008; Wing et al ., 2009). The terrestrial fossil vertebrates from the Cerrejn mine represent the first record for this time period from the tropics of northern South Amer ica (Fig. 1 1) Fossil vertebrates from Cerrejn were first discovered by Henry Garcia in 1994, a geologist for the coal mine. In 2004, these fossils attracted the interest of the Smithsonian Institution and Florida Museum of Natural History. Many collecti ng expeditions by dozens of individuals from 2004 through 2011 resulted in a robust
17 sampling of the vertebrate fossil fauna of the Cerrejn Formation. The first fossils collected by Garcia were of a dyrosaurid crocodyliform. Dyrosauridae represents an evol utionary cousin of the lineage that ultimately led to all modern crocodylians and their divergence occurred in the Late Cretaceous (Jouve et al., 2006). Dyrosauridae was one of the few to span the Cretaceous Paleogene extinction in South America (Gasparini 1996). They persisted and dispersed globally until their ultimate extinction in the Eocene. The vast majority of fossil dyrosaurids have come from Africa, with a few other known occurrences in North America, Asia, and South America with a mostly Tethyan dispersal (Buffetaut, 1981). Dyrosauridae had been known primarily from coastal/estuarine and shallow marine deposits from the Late Cretaceous to Eocene and to have a distinctly longirostrine skull (Buffetaut, 1981). Dyrosaurids have been recovered from fr eshwater sites, but have been small and fragmentary The small size of these fossils has been used to explain them as juveniles (Jouve et al., 2008b) Identifiable dyrosaurid remains have not been recovered from marine deposits thus far. Jouve et al. (2008) suggested that dyrosaurids were able to survive the mass extinction which dramatically affected marine ecosystems (DHondt, 2005) because unlike the coexisting sauropterygians and mosasauroids (Motani, 2009), the dyrosaurids had a part of their life cycl e in freshwater habitats (Jouve et al., 2008b). However, all but one marine Late Cretaceous species of Dyrosauridae survived into the Paleocene (Hill et al., 2008). If adult dyrosaurids inhabited freshwater at Cerrejn, it would represent a rare transition from saltwater to freshwater in a poikilothermic tetrapod.
18 Within the warm climate of ancient Cerrejn and under the circumstances of a transition from saltwater/brackish water habitat to a freshwater one, what adaptations (if any) did the Cerrejn dyrosaurids have for the new habitat, and how have they diversified relative to nonfreshwater dyrosaurids? Are there observable adaptations for a fluvial environment, or are they retaining their primitive longirostrine morphology? Given the correlation between skull shape and dietary preference (Brochu, 2001), would the availability of different prey result in new feeding adaptations reflected in skull structure? Given the behavior of the modern saltwater crocodile, Crocodylus porosus to disperse via currents ( Campbell et al., 2010), did dyrosaurids arrive in Colombia from a marine ancestor by similar methods and how might past continental positioning and oceanic temperatures have affected th eir dispersal? The hypotheses for these questions that are the impetus of this dissertation are that d uring the warm Paleocene, dyrosaurids inhabited freshwater into adulthood and are morphologically distinct from their nonfreshwater counterparts resulting in adaptions for increased terrestriality and new prey types (i.e. ne w skull shapes). Furthermore the dyrosaurids took advantage of warmer currents following past North Atlantic circulation and dispersed largely along coasts and across narrow seaways. The tests for these hypotheses are to use all identifiable fossils available to establish the differences and similarities between the freshwater dyrosaurids of Cerrejn and nonfreshwater dyrosaurids. The tests for these hypotheses utilize alpha taxonomy, cladistic analyses, biogeography, and functional morphology, and geometr ic morphometrics to fully understand morphological change to better understand transitions in habitat in this extinct poikilothermic tetrapod.
19 Initial study of the crocodyliform fossils from Cerrejn revealed at least three new genera and species of Dyrosauridae. When a new fossil taxon is described, it is essential to provide a thorough diagnosis and description and assign a holotype and any referred material As such, large sections of three chapters of this dissertation are devoted to detailed morphologi cal description of these new taxa. This dissertation is broken into six chapters. The first, this introduction, is followed by three successive descriptions of each new species of Dyrosauridae. Each of these chapters includes morphological and systematic d escriptions necessary for the proper naming of new taxa. Each chapter also includes phylogenetic analyses, biogeography (and functional morphology in Chapters 3 and 4) with comparisons to nonfreshwater dyrosaurids. The fifth chapter is a synthetic study o f dyrosaurid and extant crocodylian morphospace as well as diversity studies of marine taxa from the Late Cretaceous through Eocene. The aim of the fifth chapter is to address the over arching questions of morphological adaptation in the Cerrejn dyrosauri ds within the context of the rest of Dyrosauridae and all modern crocodylians in terms of quantifiable differences .The diversity studies address the question of why dyrosaurid diversity has risen and fallen through geologic time by comparing to diversity of potential sources of competition and testing for statistical correlation. The sixth chapter is conclusions and remarks. Chapters 2 and 3 were published in 2010 and 2011, and as such their new scientific names are included ( Cerrejonisuchus improcerus and Acherontisuchus guajiraensis ) These significant contributions to the dissertation are reprinted with permission from their respective journals of publication. The third new genus and
20 species is not mentioned by its new scientific name as it has not yet been published, and is instead referred to simply as Unnamed Taxon.
21 Figure 11. Paleocene map of all fossil vertebrate localities reported in the Paleobiology Database as of April 26, 2012 Yellow star indicates Cerrejn fossil locality. Blue dots indicate other Paleocene vertebrate fossil localities.
22 CHAPTER 2 A NEW SMALL SHORT SNOUTED DYROSAURID ( CROCODYLOMORPHA, M ESOEUCROCODYLIA) FRO M THE PALEOCENE OF N ORTHEASTERN COLOMBIA I ntroduction Dyrosauridae is an extinct family of mesoeucrocodylians typically f ound in transitional marine sediments from the Late Cretaceous through Late Eocene (Brochu et al., 2002)1. The family was named by Giuseppe De Stefano in 1903 for the type genus Dyrosaurus named by A. Pomel for the locality of the holotype, Djebel Dyr, near Tbessa, Algeria (Pomel, 1894). Dyrosaurid crocodyliforms are well known from the Late Cretaceous to Eocene of northern Africa and southwestern Asia (e.g. Swinton, 1930, 1950; Arambourg, 1952; Halstead, 1973, 1975; Halstead and Middleton, 1976; Buffetaut 1976a, 1976b, 1977, 1978 a 1979, 1980; Storrs 1986; Buffetaut et al., 1990; Langston, 1995) as well as the Late Cretaceous to Paleocene of eastern North America (e.g. Troxell, 1925; Parris 1986; Denton et al., 1997), and possibly the Late Cretaceous of E urope (Buffetaut and Lauverjat, 1978). However, the fossil record of dyrosaurids in South America is more limited. Fossils of dyrosaurid crocodyliforms have previously been recovered from only four localities in South America. Hyposaurus derbianus is known from somewhat fragmentary fossils from the Maria Farinha Formation in Pernambuco, Brazil (Cope 1885, 1886). The Maria Farinha Formation was originally thought to be Late Cretaceous (Cope, 1885, 1886; Buffetaut, 1976a, 1980), but has been more recently placed in the Paleocene (Alberto et al., 1993). Argollo et al. (1987) described a Late Cretaceous or 1 Reprinted with permission from Hastin gs, A. K., Bloch, J. I., Cadena, E.A., Jaramillo, C.A. 2010 A new small short snouted dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of northeastern Colombia. Journal of Vertebrate Paleontology 30: 139 162.
23 Paleocene crocodyliform assemblage from Huarachani in Bolivia that included two teeth, two osteoderms, and a vertebra attributed to Dyrosauridae gen. et sp. indeterminate. Marshall and de Muizon (1988) produced a faunal list from Tiupampa, Bolivia, that included a crocodyliform referred to the dyrosaurid Sokotosuchus aff. ianwilsoni and thought to be Late Cretaceous in age. Fossils from this site were later re ferred to Dyrosauridae gen. et sp. indet. and considered Paleocene in age (Buffetaut, 1991). A mandibular symphysis of Sulcusuchus erraini from Patagonia was attributed to Dyrosauridae (Gasparini and Spalletti, 1990; Gasparini, 1996), but was later referred to Plesiosauroidea (Gasparini and de la Fuente, 2000) outside of Crocodylomorpha (Gasparini, 2007). Additional dyrosaurid specimens from the Paleocene part of the Maria Farinha Formation have been found from the same unit that H. derbianus was discovered, including some isolated teeth and vertebrae (Carvalho and Azevedo, 1997; Gallo et al., 2001). Barbosa et al. (2008) also recently described a new genus and species, Guarinisuchus munizi, based on a complete skull and partial lower jaw from the Maria Fari nha Formation. Most of these sites are south of the ancient tropical zone (Scotese, 2001; Fig. 2 1). Thus very little is known of the diversity of Dyrosauridae within South America, and little is known of crocodyliforms as a whole for the ancient neotropic s prior to the Eocene. Here I describe dy r osaurid fossils from the Cerrejn coal mine in northeastern Colombia (Bloch et al., 2005; Hastings and Bloch, 2007, 2008). The fossil bearing locality outcrops in the La Puente Pit and is situated in the underclay of Coal Seam 90 in the Cerrejn Formation. The age of the Cerrejn Formation has been estimated to be middle late Paleocene based on carbon isotopes, pollen, spores, and dinoflagellate
24 cysts (Fig. 2 2 ; Jaramillo et al., 2007). The surrounding matrix is com prised of bituminous coal and gray, finegrained clay. The paleoenvironment of the section from which the fossils were recovered is transitional, with likely brackish water in a riverineto lagoonal setting. The environmental conditions implied by the geol ogy of the site, as well as associated faunas including large freshwater turtles, a giant boid snake, and dipnoan and elopomorph fishes (Bloch et al., 2008; Head et al., 2009), are consistent with a transitional marinefreshwater environment. The environment of the dyrosaurids in Colombia is likely more inland than the estuarine environment of the dyrosaurid locality within the Umm Himar Formation of Saudi Arabia (Langston, 1995), but nearer to the coast than the fluvial setting of the northern Sudan dyrosaurid locality (Buffetaut et al., 1990). D escribe d here is a new dyrosaurid based on three skulls, a lower jaw, and associated postcrania. Another ten individual crocodyliforms, represented by at least somewhat complete cranial or mandibular material of at least two additional taxa of very different morphotypes have also been recovered from the Cerrejn Formation (e.g., Hastings and Bloch, 2008) and will be described elsewhere. Institutional Abbreviations AMNH, American Museum of Natural History; IGM, Museo Geolgico, at the Instituto Nacional de Investigaciones en Geociencias, Minera y Quimica, Bogot, Colombia; UF, Florida Museum of Natural History, University of Florida; YPM, Yale Peabody Museum. Terminology and Anatomical Abbreviations Teeth and alveoli will be referred to by number with 1 being the most anterior. Premaxillary teeth and alveoli will have the initial pm, maxillary teeth and alveoli will
25 use m, and dentary teeth and alveoli will use d. For example, the first tooth or alveolus of the p remaxilla will be referred to as pm1 and the second tooth or alveolus of the maxilla will be referred to as m2. This nomenclature is modified from Sereno et al. (2001) and de Lapparent de Broin (2002). Systematic P aleontology C rocodylomorpha, Walker, 1 970 C rocodyliformes Hay, 1930 M esoeucrocodylia, Whetstone and Whybrow, 1983 D yrosauridae, de Stefano, 1903 C errejonisuchus G en. N ov. Etymology Named for the Cerrejn Formation from which the fossils were recovered within the Cerrejn coal mine on the G uajira Peninsula of northeastern Colombia and suchus Greek for crocodile. Type and o nly k nown s pecies. Cerrejonisuchus improcerus Range From the middle to late Paleocene of Colombia. Diagnosis As for the type and only known species, Cerrejonisuchus improcerus Cerrejonisuchus improcerus, S p. N ov. Etymology improcerus Latin for diminutive, an allusion to not only its relatively short snout, but also its relatively small body size. Holotype UF/IGM 29, a nearly complete skull including the entire snout, 11 teeth, a complete dorsal skull table (postorbital, squamosal, parietal, and frontal) and a partial occipital region including exoccipitals, basioccipital, and partial basisphenoid. Type l ocality and h orizon. All known specimens are from the Cerrejn Fo rmation, underclay of Coal Seam 90 at the La Puente Pit within the Cerrejn Coal
26 Mine in Northeastern Colombia. Middle to Late Paleocene in age. Latitude 11.08.45.50 N, longitude 72. 32.55.56 W. Referred s pecimens. UF/IGM 30, lower jaw including dentaries and splenials and a total of 11 partial teeth. Latitude 11.08.38.93 N, longitude 22.214.171.124 W. Additional unprepared fossils include: UF/IGM 31 a nearly complete skull with at least four teeth and associated postcranials including a humerus, ulna, left fem ur, fibula, tibia, left and right pubi, 17 vertebrae, one rib, and 8 osteoderms; UF/IGM 32, a complete snout and partial orbital region. Diagnosis Shorter snout, approximately 5459% of the dorsal skull length, than that of all other known dyrosaurids. Al so differs from all other dyrosaurids in having approximatly 11 teeth in each maxillary, 8 of which are anterior to the orbits. Further differs from all known dyrosaurids except Chenanisuchus in having a wide interfenestral bar that is squareshaped in cross section. Further differs from all other dyrosaurids except Phosphatosaurus (and possibly Arambourgisuchus ) in having a reduced fourth premaxillary tooth. Further differs from Phosphatosaurus and Sokotosuchus in lacking a festooned lateral margin of th e snout in dorsal view. Further differs from Hyposaurus Rhabdognathus Atlantosuchus and Guarinisuchus in having a mediolaterally straight posterodorsal margin of the parietal. Further differs from Chenanisuchus and Sokotosuchus in having well developed occipital tuberosities. Further differs from Chenanisuchus in having ornamentation continuous across dorsal and lateral surfaces with no interruption across sutures and orbits medially and dorsally placed, most closely approximating the orbit position of Dy rosaurus Further differs from Hyposaurus rogersii in having teeth with straight, rather than twisted anterior carinae.
27 Preservation While t he type specimen (UF/IGM 29) is slightly dorsoventrally compressed, it is a nearly complete skull preserving most cr anial elements from the terminus of the premaxillae to the occipital condyle with many features preserved in three dimensions (Figs. 2 3 and 2 4). The posterior portion of the palatines, both pterygoids, both ectopterygoids, the internal choanae, prootic bones, and quadratojugals are missing in UF/IGM 29 (Fig. 2 5). The lateral margin of the right quadrate is missing, as is the posterior portion of the jugal. Description General Unless otherwise noted, all descriptions and measurements are taken from the holotype (UF/IGM 29; Figs. 2 3 through 2 5). The snout is relatively narrow and comprises about 5459% of the dorsal skull length, measured from the tip of the snout to the posterior margin of the parietal (Table 2 1). The lateral margins of the snout remai n parallel in dorsal view from the external nares to anterior to the orbits (Fig. 2 3). Ornamentation consists of shallow pits consistent on the dorsal surfaces (Fig. 2 3) as well as the preserved lateral surfaces of the specimen (Fig. 2 4A), and is consis tent across cranial bone sutures. Cranial o penings The external nares are mediolaterally oval, oriented dorsally, and surrounded exclusively by the premaxillae (Fig. 2 3). The external nares are located extremely anteriorly, with only a thin wall (6.57 m m) of the premaxillae around the anterior edge. These conditions are consistent across all specimens and are not likely the result of deformation. The anterior lateral margins are angled toward the midline of the snout. The lateral margins of the external nares are approximately level with the posterior and anterior margins, and do not slope ventrally or dorsally (Figs. 2 3, 2 4A).
28 Two low ventral ridges extend posteriorly from the anterior margin of the external nares, paralleling what would have been the midline of the snout (Fig. 2 3). At the posterior end of the external nares are two small tubercles on the ventral surface of the external nares projecting from the posterior wall (Fig. 2 3). These tubercles are also present, but partly eroded, in UF/IGM 31 and 32 (Figs. 2 6 and 2 7), and therefore the feature seems representative of the species. Due to anteroventral flattening, the incisive foramen has been displaced laterally from the midline of the external nares (Fig. 2 5). The incisive foramen is entir ely surrounded by the premaxillae. The incisive foramen is visible in dorsal view through the external nares as a small pit between the low anterior ridges (Fig. 2 3). In ventral view, the foramen has a triangular anteriorly directed process placed mediall y over the foramen, between the pm1 teeth (Fig. 2 5). The entire foramen is level with the pm2 alveoli. The orbits of UF/IGM 29 are oval in outline and oriented anterodorsally, near the midline (Figs. 2 3, 2 4A). The prefrontals participate in the anteromedial corners of the orbits. The lateral margins of the orbits are comprised of the lacrimal, with the jugal only participating in the posterolateral corners. The medial margins of the orbits are entirely comprised of the frontal bone. The posterior margins of the orbits are slightly more than half comprised of the postorbitals that have prominent anterolateral processes. Less than half of the remaining posterior orbital margins are formed by the frontal (Fig. 2 3). The separation between the orbits by the f rontal is approximately one third the width of an orbit.
29 Flattening has distorted much of the infratemporal fenestrae of the holotype (Fig. 2 4A). However, UF/IGM 31 has preserved the left infratemporal fenestra (Fig. 2 6). This fenestra is elongate, anter oposteriorly longer than it is dorsoventrally wide. The postorbitals constitute the anterodorsal portions of the fenestrae. Along the ventral margins of the infratemporal fenestrae the jugals rise dorsally at a point nearly even with the postorbital squamo sal joint and approximately halfway along the margin (Figs. 2 4A, 2 6) The posterodorsal corner in UF/IGM 31 is bound by the quadratojugal (Fig. 2 6). The supratemporal fenestrae are 51.8% longer than they are wide and narrow anteriorly to 63.7% of the width across the posterior fenestrae (Fig. 2 3). The anterior and posterior margins of the supratemporal fenestrae are rounded, making the fenestrae longitudinally ovular with a straight medial margin, and lateral margins that taper anteriorly toward the midl ine. The fenestrae are bound anteromedially by the frontal. The postorbitals constitute the lateral halves of the anterior margins as well as the anterior halves of the lateral margins. The parietal forms approximately the medial three quarters of the post erior margins of the supratemporal fenestrae. The posterior halves of the lateral margins, as well as the remaining one quarter of the posterior margins, of the fenestrae are bound by the squamosal. The posterior walls of the supratemporal fenestrae are weakly sloped anteroventrally from the skull roof and are largely visible in dorsal view (Fig. 2 3). This feature may have been exaggerated slightly from dorsoventral flattening, but a significant amount of exposure is evident even in the less flattened spec imens. The interfenestral bar is very wide, 24.60 mm at its widest and 16.71 mm at its narrowest. The cross section of the interfenestral bar is rectangular in shape, and not T shaped.
30 The temporal canals have largely been lost. The right parietal squamosal suture is incomplete and slightly separated with a subtle widening of a crack (0.40 mm) at roughly the expected level of the temporal canal. This depression likely represents the cavity that was the temporal canal and is dorsolaterally bound by the squam osal and medioventrally bound by the parietal. The posttemporal fenestrae are located dorsal to the occipital tuberosities and are oriented mediolaterally, and parallel to the skull roof (Fig. 2 4). The posttemporal fenestrae are typically dorsoventrally short among dyrosaurids (Jouve, 2005), but due to taphonomic dorsoventral distortion, this characteristic has been further exaggerated. The fenestrae are bound dorsolaterally by the squamosals and dorsomedially by the parietal. The ventral surface is formed by the occipital tuberosites of the exoccipitals. The supraoccipital is not complete, but evidently had little to no participation to the posttemporal fenestrae. Much of the palatines have been crushed and/or lost, and both ectopterygoids are absent, thus little can be discerned of the suborbital fenestrae (Fig. 2 5). A small portion of the medial and anterolateral margins of the right suborbital fenestrae remain. The preservation of the right suborbital fenestra includes the anterolateral margin formed by the maxilla, and ceases anteriorly at the anteromedial corner, comprising about twothirds of the anterior margin of the fenestra. This margin is round and smooth with a slight protrusion of the palatine into the fenestra in the middle of the medial margin near the m9 alveolus (Fig. 2 5). The fenestra reaches anteriorly to the level of the m8 alveolus. In addition, onethird of the anteromedial margin margin of the left suborbital fenestra is also present, where the palatine has been flattened so that it i s
31 flush dorsally against the braincase. Posteriorly the preservation of the left suborbital fenestra ceases with the posteriormost preservation of the left maxilla, which is at the level of the m11 alveolus. The suborbital fenestrae are narrow and slender in shape and anteriorly acute. The suborbital fenestrae are very posteriorly placed, and their anterior margins do not reach the level of the orbit. The foramen magnum has been crushed dorsoventrally, only leaving a shallow depression (Fig. 2 4B). The foramen is bound laterally and dorsally by the exoocciptals, comprising threequarters of the margin. The ventral margin is formed by the basioccipital. Premaxillae. The premaxillae are well preserved in UF/IGM 29. The anterior end of the snout has been dorsov entrally compressed with slight warping toward the left side (Figs. 2 3, 2 5). This has resulted in five premaxillary teeth displaced from, but still adjacent to, their respective alveoli (Fig. 2 5). The premaxillae do not expand laterally with respect to the maxillae. The premaxillamaxilla suture is level with the pm3 alveoli on the dorsal and ventral surfaces (Figs. 2 4, 2 5). The posterodorsal process extends posteriorly to the interalveolar space between the m1 and m2, and penetrates between the maxill ae and nasal (Fig. 2 3). Four alveoli are present on each premaxilla. The left pm1 tooth is notably shorter in length from the right (8.44 mm vs. 15.43 mm), likely due to different stages in replacement. The teeth of pm1 are placed very close together (2.1 1 mm apart). A deep gap is present between the pm1 and pm2 alveoli, large enough for lower dentition to occlude. These deep notches are visible on the dorsal surface as slight indentations along the anteromost margin of the snout (Fig. 2 3). The pm3 alveol i are notably raised from the adjacent alveoli and much more robust (Fig. 2 -
32 4A). Measurements of alveolar size and spacing are provided in Table 22 The premaxillae have shallow pitted ornamentation, with anterior ornamentation directed toward the midline Maxillae The maxillae of UF/IGM 29 comprise most of the snout. The left maxilla has 11 preserved alveoli, the right maxilla has nine variably preserved alveoli (Fig. 2 5). The terminal end of the left maxilla represents the end of this bone posteriorly where it would have fused with the ectopterygoid that was not preserved. An indentation is present just posterior to the premaxillamaxilla suture along the lateral snout margin, visible in both dorsal and ventral views, particularly on the right side (Fig s. 2 3, 2 5). The maxillae have smooth, even margins that gradually expand posterolaterally (Fig. 2 3). The maxillae are dorsally separated by the nasal (Fig. 2 3). The two maxillae contact each other posteriorly until the level of the interalveolar space between m4 and m5 where the maxillae are medially separated by the palatines and extend posterolaterally. Posteriorly, the maxillae extend to the level of the posterior margins of the supratemporal fenestrae, with the posteromost alveolus being just anteri or to this level. In addition, the maxillae contribute posteriorly to the anteroventral portion of the lower temporal bar (Fig. 2 4A). The alveoloar walls project ventrally, forming raised walls above the interalveolar space. A deep sulcus is located just anterior to the m1 alveolus (Fig. 2 5). Of the preserved dentition, the m3 alveoli are by far the largest. Interalveolar spaces are fairly consistent, and typically less than onethird the length of the adjacent alveoli. D eep sulci are present between the m4 and m5 alveoli, deeper than those between the pm4 and m1. Smaller, yet still deep, occlusal pits are found between the m3 and m4 alveoli as well as between the m5 and m6 alveoli. The maxillary alveoli are
33 mostly circular in outline, but especially posteriorly they have a slight tendency toward an anteroposterior ovate shape. Table 22 provides alveolar size and spacing. A small ridge is visible in ventral view along the suture between the left and right maxillae (Fig. 2 5). The maxillae are dorsally and laterally ornamented (Figs. 2 3 and 2 4A). Nasal The nasals are fused in UF/IGM 29 (Fig. 2 3) and UF/IGM 31 (Fig. 2 6), but are clearly unfused in UF/IGM 32 (Fig. 2 7). As UF/IGM 29 and 31 are similarly sized, and UF/IGM 32 is slightly smaller, this character may be related to ontogeny. The single nasal of UF/IGM 29 gradually widens from its anterior point to 12.99 mm at its posteriormost contact with the premaxilla. The nasal contacts the premaxillae dorsally at the level of the pm3 alveolus. Anteriorly, the nasal comes to a point near the narial opening, with only a small space (20.46 mm) along which the premaxillae fuse together before the posterior margin of the external nares, such that the nasal does not participate in the posterior margin of the external nares (Fig. 2 4). The width is relatively constant from this point of contact with the premaxilla (13.03 mm wide) until the first point of contact with the lacrimal (15.70 mm wide) a 17% increase in width. The area where the nasal joins the frontal, l acrimal, and prefrontal is distorted, with the posterior end of the nasal overlapping the anterior end of the frontal bone. The posterior end of the nasal terminates at the level of the m5 alveoli. Due to lack of preservation, whether or not the nasal bifurcates into two posterior processes cannot be discerned in UF/IGM 29. The posterior nasals are better preserved in UF/IGM 31 and 32 and do not bifurcate (Fig. 2 7). The nasal does not contact the orbit in either UF/IGM 29 or UF/IGM 32. The ornamentation of the nasal is relatively shallow and uniform.
34 Prefrontals The size disparity between the prefront als of UF/IGM 29 and 31 is 47% (~16.7 mm anteroposterior length in UF/IGM 29 and 34.8 mm in UF/IGM 31) despite only a 17.8% difference in skull length (Table 2 1). The prefrontals of UF/IGM 32 are incomplete, but appear more similar to the large condition seen in UF/IGM 31. In all specimens, both prefrontals have a straight contact with the frontal, parallel to the midline. Lacrimals The left lacrimal of UF/IG M 29 is more complete than the right and bears a very prominent long and narrow ridge ascending from its contact with the left jugal. A portion of this long, narrow ridge is present on the right side, but neither its contact with the jugal, prefrontal, or nasal is preserved. The prominent lateral ridge composing the lateral margin of the orbit widens posterolaterally. The lacrimal constitutes most of the lateral margin of the orbit, with the jugal comprising only the posteromost portion. The lacrimal expands anteriorly and curves medially toward the midline, constituting much of the semicircular anterior margin of the orbit. The lacrimal extends anteriorly to the level of the m4 alveolus. The left lacrimals length of contact with the prefrontal, 14.65 mm, i s greater than that with the nasal, 10.72 mm. The ornamentation of the lacrimal is limited to the lateral surface. Frontal The single cruciform frontal of UF/IGM 29 is nearly complete, except where the frontal nasal suture was not preserved (Fig. 2 3) and whether or not the frontal penetrates the nasal is unclear. The frontal reaches farther than the prefrontals anteriorly (Figs. 2 3 and 2 6). The frontal participates in the anterior 28% of the thick interfenestral bar. In cross section, the anterior projection of the frontal is roughly triangular, with the point directed ventrally, and is roughly as wide as the interfenestral
35 bar. The frontal contributes to the margins of both orbits and both supratemporal fenestrae. The bone comprises the entire medial margin of the orbit as well as the medial half of the posterior margin (Fig. 2 3). The suture with the postorbital is at the midline of the orbit. The participation of the frontal to the posteromedial corner of the orbit is a smooth, semicircular curve. The parietal frontal contact occurs along the dorsal surface of the interfenestral bar and extends anterolaterally and ventrally through the supratemporal fenestra. The contact with the laterosphenoid is located anterior to the dorsal frontal parietal suture. The anteromedial margin of the supratemporal fenestra formed by the frontal is slightly overhung. However, the interfenestral bar is barely overhung. On the ventral surface of the anterior portion of the frontal is a shallow midline groove, visible near the midline, indicating the pathway for the olfactory tract (Brochu et al., 2002). The ornamentation of the frontal is shallowly pitted, present at sutures, and oriented anteroposteriorly (Fig. 2 3). Two faint shallow grooves can be discerned extending just anterior to the supratemporal fenestral margin in an anteromedial direction, ceasing anteriorly about level with the posteromedial corners of the orbits. Parietal The interfenestral bar is slightly crushed at the contact between the frontal and parietal, with the posterior margin of the frontal being uplifted onto the anterior margin of the parietal (Fig. 2 3). The parietal portion of the interfenestral bar is equally as thick as that portion of the frontal, and comprises 72% of the length of the interfenestral bar. The interfenestral bar is roughly square in cross section, with slight overhang on the dorsal surface. The thickness of the interfenestral bar is 16.71 mm at the closest point to the frontal that gradually thickens to 24.60 mm at its base at the
36 posterior margin of the supratemporal fenestrae. The anteroventral portion of the parietal within the right supratemporal fenestra has been pushed up relative to the rest of the parietal, overlaying its otherwise smoothly dipping surface and obscuring its suture with the laterosphenoid (Fig. 2 3). The parietal overhangs anterodorsally onto the posterior margin of the supratemporal fenestra. The overhang originates at the parietal squamosal suture and deepens toward the midline, where it merges with the ver y slight overhang of the interfenestral bar. This is less pronounced than the overhang in the anteromedial corners of the supratemporal fenestrae by the frontal bone. The parietal quadrate suture is parallel with the skull roof, and is not visible in dorsal view. The parietal squamosal suture extends laterally from the point of the posterior margin of the supratemporal fenestra, and passes through the location of the presumed temporal canal, slightly lateral to the midwidth of the supratemproal fenestra, and continues to extend ventrolaterally. The right parietal squamosal suture is relatively straight, without a zigzag pattern, but the left suture is too distorted to be certain. The posterior portion of the parietal comprising the skull roof contacts the l eft and right squamosals and forms the posterior margin of the supratemporal fenestrae is broad, thick, and flat anteroposteriorly and transversally straight (Fig. 2 3). The parietal is dorsoventrally thin, slopes gently posteroventrally, and is slightly exposed in occipital view (Fig. 2 4B). A small process projects ventrally, visible in posterior view, that has a raised midline and depression on either side such that it forms a thin ridge projecting ventrally from the skull roof (Fig. 2 4B). The parietal supraoccipital suture is crescentic, and not W shaped. The parietal is ornamented evenly across its dorsal surface, including across the suture with the frontal on the interfenestral bar (Fig. 2 3).
37 Postorbitals The right postorbital has better preservation than the left and is essentially complete (Fig. 2 3). The postorbital constitutes the anterolateral margin of the supratemporal fenestra, and the posterior margin of the orbit (Fig. 2 3). The right postorbital has a strong anterolateral ventrally dire cted process that contacts the jugal and marks the posterolateral corner of the orbit. The postorbital frontal contact occurs roughly at the midwidth of the anterior dorsal margin of the supratemporal fenestra. The posterior extensions of the postorbitals extend to about one third the length of the supratemporal fenestrae from the posterior edge (Fig. 2 3). As the infratemporal fenestrae are incomplete, the amount of participation of the postorbitals can only be estimated, but is likely less than half of t he dorsal margin (Figs. 2 4A and 2 6), and whether or not it contacts the quadratojugal is uncertain. The postorbital bars have been crushed beneath the frontal and postorbitals, and little can be discerned of their thickness or relative participations of the postorbital and jugal. The postorbitals have similar ornamentation to the rest of the dorsal surface of the skull and ornamentation continuous across sutures (Fig. 2 3). Squamosals The squamosal parietal contact occurs at the midwidth of the posteri or margin of the supratemporal fenestra (Fig. 2 3). The squamosal postorbital suture occurs roughly in the middle of the supraoccipital fenestrae. The squamosal narrows slightly anteriorly toward the suture with the postorbital, and is thick posteriorly, a long the posttemporal bar (Fig. 2 3). The squamosal contacts the postorbital ventrally, participating in the posterodorsal margin of the infratemporal fenestra (Fig. 2 4A). The lateral margin of the squamosal bears a faint groove that does not flare anteri orly (Fig. 2 4A). The squamosal terminates posterodorsally in a short posteriorly directed process
38 that is roughly level with the posterior edge of the occipital tuberosity and the base of the occipital condyle (Fig. 2 3). The squamosal does not extend ven trally in occipital view, and its visibility in this view is limited to the dorsalmost portion (Fig. 2 4B). Ornamentation is pronounced near the parietal, but otherwise consistent across the dorsal surface of the squamosal (Fig. 2 3). Jugals The anterolat eral portion of the jugal of UF/IGM 29 is all that remains of the bone on the left side, from its contact with the lacrimal to the anterior threequarters of its participation in the infratemporal fenestrae (Fig. 2 4A). Less is preserved of the right jugal only from the presumed contact with the lacrimal to nearly the anterior half of the infratemporal fenestra (Fig. 2 3). The jugal of UF/IGM 29 only participates minimally in the posterolateral corner of the orbit. The point where the maxillary jugal and m axillary lacrimal sutures meet is at the posterolateral corner of the orbit (Fig. 2 3). The anteromost extent of the jugal is roughly level with the posterior onethird of the orbit. The lacrimal jugal contact is slanted anteroventrally posterodorsally. There is no evidence of foraminae along the jugals, thus it seems unlikely that UF/IGM 29 had a well developed anterior jugal siphonial foramen (as discussed for Rhabdognathus in Brochu et al., 2002). Supraoccipital The supraoccipital is recessed between the occipital tuberosities and only slightly contributes to the medial portion of the tuberosities (Fig. 2 4B). The supraoccipital is not V shaped, but instead more crescentic, bowing inward toward the braincase. The supraoccipital is dorsally bordered by th e parietal and medioventrally by the exoccipital. The exoccipital separates the supraoccipital from the foramen magnum.
39 The supraoccipital does not contribute to the posttemporal fenestrae or contact the squamosals. Exoccipitals The exoccipitals are mostl y preserved, yet compressed dorsoventrally (Fig. 2 4B). The bones are present along both sides of the occipital condyle, but displaced on the right side, and too distorted to make accurate measurements. Exoccipital participation to the width of the occipit al condyle may be estimated from the better preserved left side to be about 36.8% dorsally and 26.3% ventrally. The exoccipital participates to the dorsal threequarters of the foramen magnum. Dorsally, the exoccipital comprises the majority of the occipit al tuberosity, that is well developed, rounded, and directed posteriorly (Fig. 2 3, 2 4B). The exoccipital extends laterally to constitute the ventral portion of the paraoccipital process. Much of the basioccipital tubera have been crushed and lost, and participation of the exoccipitals cannot be estimated (Fig. 2 5). The left foramen vagi (X XI), that houses the vagus (X) and accessory nerves (XI) as well as the jugular vein (Brochu et al., 2002) is preserved, as well as the right carotid foramen (Fig. 2 5 ). The foramen vag us is located along the lateral margin of the base of the ocipital condyle and is directed ventroposteriorly. The exoccipital forms the entire ventral surface of the posttemporal fenestra. Basioccipital The basioccipital forms the bulk o f the occipital condyle and extends ventrally, forming the basioccipital tubera, that have mostly been lost in UF/IGM 29 (Fig. 2 4B; Fig. 2 5). The basioccipital tubera are oriented posterolaterally relative to the midline, forming a V shape in ventral view (Fig. 2 5). The tubera are of indeterminate shape in occipital view (Fig. 2 4B). There is a relatively wide, flat rugosity extending along the anteroventral midline of the basioccipital, that is more ventral than
40 the lateral edges. The ventral surface of the occipital condyle lacks any distinct grooves paralleling this rugosity (Fig. 2 4B; Fig. 2 5). Due to poor preservation in this region, it is difficult to determine how much the basioccipital extends ventrally from the occipital condyle. The area between the occipital condyle and the basioccipital tubera is arched dorsally, creating a smooth, concave outline in lateral view. Quadrates The quadrates have been crushed dorsoventrally such that they are flat and parallel to the skull roof. The right quadrate is very well preserved, reaching as far anteriorly as the level of the postorbital squamosal contact, and lies immediately ventral to the squamosal throughout its length (Fig. 2 5). The quadrates are posteroventrally oriented and the cranioquadrate canals are not preserved (Fig. 2 4A; Fig. 2 5). The condylar portion of the left quadrate is lacking the lateral portion, leaving only the medial most one third. The quadrate condyle is better preserved in UF/IGM 31, which shows a partly eroded participation of the quadratojugal to the condyles articulation with the lower jaw (Fig. 2 6). The quadrates lack a crest at midwidth which does not seem to be an artifact of preservation (Fig. 2 5). Quadratojugals The left quadratojugal is preserved in UF/IGM 31 onl y (Fig. 2 6), and comprises the posterodorsal margin of the infratemporal fenestrae. The quadratojugal quadrate suture is somewhat obscured, but includes the quadratojugal in the articulation with the lower jaw. Palatines The palatines of UF/IGM 29 have been flattened against the skull, and most of the posterior portions are missing, but clearly expand posterolaterally. The anterior portions form a sharp V between the maxillaries that reach anteriorly to the
41 interalveolar space between the m6 and m7 alveol i (Fig. 2 5). The palatine forms the medial margin of the suborbital fenestra as well as its anteromedial corner. Laterosphenoids Little identifiable material remains of the laterosphenoids. A small portion of them are visible in dorsal view in the suprat emporal fenestrae ventral and lateral to the parietal and frontal (Fig. 2 3). Much of the laterosphenoids in ventral view are obscured by the palatines crushed upon them (Fig. 2 5). A small anterior portion is exposed, in which the sutures of the parietal and frontal are parallel with the skull roof. The laterosphenoid does not contact the squamosal. Basisphenoid. The ventral portion of the basisphenoid that includes the basisphenoid rostrum is missing (Fig. 2 5). The posterior branch of the medial eustachi an foramen is visible in ventral view roughly 2 mm anterior to the ventral most point of the basisphenoid that surrounds it entirely. The medial eustachian foramen has a diameter of 1.41mm. Mandible A fairly complete mandible, UF/IGM 30 (Fig. 2 8), was re covered approximately 740 m from the site where UF/IGM 29 was discovered, within the same stratigraphic level. Based on its size, proportions, and number of teeth corresponding to the upper dentition, it is referred to Cerrejonisuchus improcerus gen. et sp nov. UF/IGM 30 likely represents a second individual due to the distance between fossil localities that the mandible is slightly smaller than would be expected for UF/IGM 29. The preservation of the mandible is very similar to that of UF/IGM 29; it has been dorsoventrally flattened toward the left lateral direction. Due to dorsoventral flattening, the height and width of the symphysis and splenials is too compressed for meaningful description or comparison.
42 The specimen includes most of both dentaries and much of the splenials, but is missing the articular, angular, and surangular bones (Fig. 2 8). The d3 13 alveoli are present on the left dentary, and the d2 13 alveoli on the right dentary. The d1 alveoli on both dentaries are damaged, however only a smal l part of the anteromost mandible is missing. The anteromost end of the right dentary suggests that the d1 alveolus for this tooth would have faced anterodorsally, not directly dorsal. The anterior portion of the mandible is not expanded, but rather continuous along most of the length of the symphysis (Fig. 2 8). The tooth of the d2 alveolus on the right dentary is flattened, but reduced relative to the space where the d1 alveolus would have existed. Measurements of the alveolar diameter and interalveolar s paces of UF/IGM 30 are compiled in Table 22 The d4 alveoli are the largest in the lower jaw and have dorsally higher alveolar walls. The dentition corresponds to the upper jaw of UF/IGM 29, such that the enlarged d4 teeth could occlude in the large inter alveolar spaces between the p4 and m1 teeth. The large diastema between the d2 and d3 teeth would correspond well with the enlarged pm3 teeth. The m3 teeth would occlude well in the large interalveolar space between the d6 and d7 alveoli. The d7 alveoli ar e only slightly reduced relative to d8. The spreading angle of the dentaries measured at the labial midpoint of the left and right d13 alveoli to the anterior terminus of the splenials is approximately 40.7o. Ornamentation along the lateral and ventral sur faces is weak. The splenials fuse along the symphysis and taper anteriorly to a wedge between the two dentaries The splenials end anteriorly at the interal veolar spaces between d6 and d7 (Fig. 2 8). The splenials extend posteriorly beyond the last tooth at d13, as seen on the left dentary. The level at which the symphysis ends posteriorly is estimated to be level with the d9 teeth. The left d13
43 alveolus supports the final tooth in the lower dentition. The anterior alveoli are oriented dorsally and slightly anteriorly, grading to more dorsally directed alveoli and teeth toward the posterior end of the jaw. Dentition Seven teeth were found in association with the maxilla, five of which were essentially preserved in place: the left and right m4, as well as the left m6 8 (Fig. 2 5). The premaxilla has preserved the right and left pm1 teeth, right and left pm3 teeth, and fragments of the right and left pm4. The posterior maxillary dentition is not preserved. UF/IGM 30 possesses an extremeley crushed and distorted right d2 tooth, very worn left d6 8 teeth, a misplaced tooth that may be referred to the right d9 alveolus, worn left d10 13, and worn right d11 12 (Fig. 2 8). The maxillary dentition of UF/IGM 29 is relatively homodont. The only significant deviations i n size are the enlarged m3 alveoli and the reduced m4 alveoli (Fig. 2 5). Their general shape is conical and labiolingually compressed. The preserved teeth have a relatively rounded apex. The teeth are defined labially and lingually by strongly developed anterior and posterior carinae. Striae are not discerni ble on either surface of the teeth. Crenulations are present on at least the lingual side of the crown of the left m7 tooth, but preservation for the other teeth is too poor to assess this feature on th e other maxillary teeth. The teeth do not increase or decrease in size posteriorly based on alveolar diameter, but without posterior teeth, it is difficult to be certain. The premaxillary tooth roots are more narrow and comparable to the apex width. In general the premaxillary teeth are thinner and longer than those of the maxillary. The maxillary tooth roots are wide relative to the crowns. The teeth do not curve distally. No preserved teeth possessed a twisted carina.
44 Comparison The elongate supratempor al fenestrae, posteriorly directed occipital tuberosities formed by the exoccipitals, strong participation of the exoccipitals to the occipital condyle, and the reduction of the seventh mandibular tooth and close placement to the eighth are major qualifying characters that unite Dyrosauridae (Jouve et al., 2006). The presence of all these characters in all preserved specimens indicates that Cerrejonisuchus improcerus belongs to Dyrosauridae. Snout proportions vary among Dyrosauridae. UF/IGM 29 and 31 posses s the shortest snout in proportion to the dorsal skull length of all known dyrosaurids (Table 2 1), at 59.30% and 54.78% respectively. Chenanisuchus lateroculi (Jouve et al., 2005a) has the second shortest snout within Dyrosauridae at 63.37%. The incisive foramen is described for Dyrosaurus maghribensis as being heart shaped and the posterior border as being comprised of the maxillae, as opposed to V shaped and entirely surrounded by the premaxillae, as in C. improcerus (Figs. 2 3, 2 5). The orbits of C. im procerus are placed much closer to the midline than those of Chenanisuchus lateroculi and the interorbital space is relatively small, more like the condition seen in D. phosphaticus The orbits are more oval in shape than the circular shape of D. phosphati cus (Jouve, 2005) and Guarinisuchus munizi (Barbosa et al., 2008). The supratemporal fenestrae of C. improcerus (Fig. 2 3) are similar to all other known dyrosaurids in being much larger than the orbits (Buffetaut, 1979) and longer than they are wide (Jouv e et al., 2005b). The separation of the supratemporal fenestrae of C. improcerus is wide and thick, unlike the thin sagittal crest of Rhabdognathus aslerensis (Brochu et al., 2002) and Guarinisuchus munizi (Barbosa et al., 2008). The cross section of the interfenestral bar is much more consistent with the square shape of
45 Chenanisuchus lateroculi (Jouve et al., 2005a) than with the T shape of Dyrosaurus (Jouve, 2005; Jouve et al., 2006) and Atlantosuchus coupatezi ( Jouve et al., 2008a), or the smooth and narrow condition of Phosphatosaurus gavialoides (Buffetaut, 1978 a ; Moody and Buffetaut, 1981), or the V shape of Rhabdognathus keiniensis (Jouve, 2007). The posterior walls of the supratemporal fenestrae are visible in dorsal view in C. improcerus as we ll as in Rhabdognathus (Jouve, 2007), but not in Dyrosaurus (Jouve, 2005). The lateral arches of the supratemporal fenestrae are robust, not thin as in Rhabdognathus (Jouve, 2007). Cerrejonisuchus improcerus like other dyrosaurids, possesses four premaxil lary alveoli. The pm4 alveolus of UF/IGM 29 is greatly reduced, whereas in Dyrosaurus and C. bequaerti the pm1, pm2, and pm4 alveoli have similar diameters (Jouve and Schwarz, 2004; Jouve, 2005; Jouve et al., 2006). Jouve et al. (2005b) inferred that A. kh ouribgaensis also has a reduced pm4 tooth. In dyrosaurids such as Phosphatosaurus gavialoides (Buffetaut, 1978 a and 1979) and Sokotosuchus ianwilsoni (Buffetaut, 1979) the lateral margin of the snout is described as festooned, referring to the undulations in the maxillae and premaxillae corresponding to alveoli and interalveolar spaces. This character is entirely absent in C. improcerus (Fig. 2 3); the margins are very smooth, as in Chenanisuchus lateroculi (Jouve et al., 2005a), Dyrosaurus phosphaticus ( Jouve, 2005), Hyposaurus rogersii (Denton et al., 1997), and Arambourgisuchus khouribgaensis (Jouve et al., 2005b). The total maxillary tooth count of C. improcerus is 11 teeth per maxilla. This number is more similar to estimates of 12 for Hyposaurus rogersii (Denton et al., 1997), 13 for Chenanisuchus lateroculi (Jouve et al., 2005a), 1314 for Sokotosuchus ianwilsoni
46 (Buffetaut, 1979) and Guarinisuchus munizi (Barbosa et al., 2008), than 15 for Phosphatosaurus gavialoides (Buffetaut, 1978 a ), 16 for Congosaurus bequaerti (Jouve and Schwarz, 2004), 17 for Arambourgisuchus khouribgaensis (Jouve et al., 2005b), 19 22 for Dyrosaurus (Jouve et al., 2006), or 2324 of Rhabdognathus keiniensis (Jouve, 2007). The nasals are entirely fused in UF/IGM 29 and 31, but unfused in the smaller UF/IGM 32 (Fig. 7). The two conditions for nasal fusing suggest the suture fuses with ontogeny in C. improcerus The fused condition is consistent with other dyrosaurids such as Dyrosaurus phosphaticus (Jouve, 2005), Phosphatosaurus gavialoides (Buffetaut, 1978 a and 1979), Hyposaurus rogersii (Denton et al., 1997), and Congosaurus bequaerti (Jouve and Schwarz, 2004). Rhabdognathus aslerensis (Brochu et al., 2002), Atlantosuchus coupatezi ( Jouve et al., 2008a), and Sokotosuchus ianwils oni (Buffetaut, 1979) have entirely unfused nasal bones, while Chenanisuchus lateroculi has an anteriorly fused nasal bone. The anterior portion of the preserved Rhabdognathus keiniensis is fused, however the posterior portion is unpreserved (Jouve, 2007). Posteromedially, the frontal participates in the thick interfenestral bar, contrasting the thin bar of A. khouribgaensis (Jouve et al., 2005b). The frontal participates 28.5% to the interfenestral bar in UF/IGM 29, as opposed to 20% in A. khouribgaensis ( Jouve et al., 2005b) and Atlantosuchus coupatezi ( Jouve et al., 2008a), 25% of D phosphaticus (Jouve, 2005) and Rhabdognathus keiniensis (Jouve, 2007), around 29% for Phosphatosaurus gavialoides (Buffetaut, 1978a ), 33% of Chenanisuchus lateroculi (Jouve et al., 2005a) and Rhabdognathus aslerensis (Brochu et al., 2002), and roughly
47 50% in Hyposaurus rogersii (Troxell, 1925). UF/IGM 29 has a wide interfenestral bar, 16.71 mm at its minimum width, very similar to that of C. lateroculi with a value of 17 mm at its minimum width (Jouve et al., 2005a). The frontoparietal suture of C. improcerus is much straighter (Fig. 2 3) than the zigzag pattern described for D. phosphaticus (Jouve, 2005). C. improcerus lacks the V shaped groove on the dorsal surface (Fig. 2 3) as in Rhabdognathus aslerensis (Brochu et al., 2002; Jouve 2007), and also lacks the deep sulcus and dorsal bulges at the posterior end when in occipital view (Fig. 2 3B). C. improcerus also lacks the strong indentation of the posterior margin (Fig. 2 3) of the parietal as in Rhabdognathus (Jouve, 2007), Hyposaurus rogersii (Denton et al., 1997), Atlantosuchus coupatezi ( Jouve et al., 2008a), and Guarinisuchus munizi (Barbosa et al., 2008). C. improcerus does not have the W shaped parietal supraoccipital s uture, seen in occipital view of D. phosphaticus (Jouve, 2005), making it more similar to the genus Rhabdognathus (Jouve, 2007) which also lacks this character. The supraoccipital of C. improcerus does not display a V shape (Fig. 2 4B) as in Dyrosaurus (Jo uve, 2005; Jouve et al., 2006), Chenanisuchus lateroculi (Jouve et al., 2005a), and Arambourgisuchus khouribgaensis (Jouve et al., 2005b). The occipital tuberosities are mostly comprised of the exoccipitals, but medially of the supraoccipital in C. improce rus (Fig. 2 4B), and are posteriorly directed as in all dyrosaurids (Jouve et al., 2006). The occipital tuberosities of C. improcerus seem at least as well developed as the moderately developed state of D. phosphaticus (Jouve, 2005); they are much more developed than in S. ianwilsoni and C. lateroculi (Jouve et
48 al., 2005a), and most similar to the length and shape of R. keiniensis and R. aslerensis (Jouve, 2007). The lateral exoccipital forms the ventral portion of the paraoccipital process of C. improcer us (Figs. 2 3, 2 4B), as in Dyrosaurus phosphaticus (Jouve, 2005) and Dyrosaurus maghribensis (Jouve et al., 2006) and possibly other dyrosaurids as well. The ventral exoccipital contributes onethird to the basioccipital tuber in D phosphaticus (Jouve, 2005), and less than onefourth in Chenanisuchus lateroculi (Jouve et al., 2005a). The participation to the basiocciptial tuber of the better preserved left exoccipital of UF/IGM 29 is 26%, more consistent with the condition of C lateroculi (Jouve et al., 2005a). Similar participation to the basioccipital tubera is also noted in Rhabdognathus aslerensis (Brochu et al., 2002). Both C. improcerus and D. phosphaticus (Jouve, 2005) exhibit an arched interspace between the occipital tuberosity and the basioccipi tal tubera. No crest is visible on the ventral face of the quadrate of C. improcerus which does not seem to be an artifact of preservation (Fig. 2 5) The lack of crest is dissimilar to A khouribgaensis (Jouve et al., 2005b), Rhabdognathus aslerensis (Bro chu et al., 2002), and Rhabdognathus keiniensis (Jouve, 2007) which all possess a crest on the ventral side of the quadrate. Dyrosaurus phosphaticus like C. improcerus (Fig. 2 5), has a concavity at the middle of the medial margin of the suborbital fenest ra, as a result of a restriction along the midlength of the palatine (Jouve, 2005). The anterior dentition of the dentary of C. improcerus is similar to that of Arambourgisuchus khouribgaensis (Jouve et al., 2005b), Hyposarus rogersii (Troxell,
49 1925), and Dyrosaurus (Jouve, 2005; Jouve et al., 2006) in that the d2 alveoli are reduced in size and the interalveolar spaces between the d2 and d3 are greater than between d1 and d2, as well as d3 being placed very close to an enlarged d4 (Fig. 2 8). Arambourgisuchus khouribgaensis also has the raised d4 alveolar wall found in C. improcerus (Jouve et al., 2005b). The anterior orientation of the d1 alveolus of C. improcerus is similar to that of Hyposaurus derbianus (Cope, 1886) and unlike that of Dyrosaurus phosphaticus which has a more dorsal orientation. The anterior portion of the C. improcerus mandible is not expanded, and thus not spatulate as in some Hyposaurus (Jouve, 2007), but more similar to H derbianus (Cope, 1886). The mandibular symphysis ends posteri orly in UF/IGM 30 at approximately the level of the d9 alveolus (Fig. 2 8) which is dissimilar to the d12 of Hyposaurus rogersii reported by Jouve (2007). This condition of the mandibular symphysis contrasts more strongly with that of other dyrosaurids whi ch have longer mandibles, such as the d14 alveolus in Guarinisuchus munizi (Barbosa et al., 2008), the d15 in Hyposaurus sp. (Jouve, 2007) and Hyposaurus derbianus (Cope, 1886), the d16 in Congosaurus bequaerti (Jouve and Schwarz, 2004) and Arambourgisuchus khouribgaensis (Jouve et al., 2005b), the d17 in Dyrosaurus (Jouve, 2005), and beyond the d19 alveolus in Rhabdognathus (Jouve, 2007). The splenials end anteriorly at the interalveolar space between the d6 and d7 alveoli in C. improcerus (Fig. 2 8), sim ilar to that of Hyposaurus rogersii for which they end at the d7 alveolus (Jouve, 2007). This splenial alveolus relationship contrasts that of other dyrosaurids with more posterior positions such as the interalveolar space between the d9 and d10 alveoli in Congosaurus bequaerti (Jouve and Schwarz, 2004)
50 and Phosphatosaurus gavialoides (Buffetaut, 1978a), the interalveolar space between d10 and d11 in Arambourgisuchus khouribgaensis (Jouve et al., 2005b) and Hyposaurus derbianus (Cope, 1886), and d12 in Dyro saurus (Buffetaut, 1978a). The overall dentary tooth estimation for H. rogersii is as high as 1720 (Buffetaut, 1980) but as low as 15 (Denton et al 1997), somewhat comparable to the 13 of C. improcerus The size of the d7 alveolus is much more comparabl e to the d8, contrary to the very reduced d7 alveolus relative to the d8 character traditionally used as a synapomorphy of Dyrosauridae. Cerrejonisuchus improcerus lacks the festooned appearance (Fig. 2 8) of H. rogersii along the lateral margins of the dentaries. Due to the flattening of UF/IGM 30 the diagnostic characters of width as compared to height of the lower jaw cannot be discerned. The apices of the crowns of the preserved teeth of UF/IGM 29 are more rounded than acute, as in C bequaerti (Jouve and Schwarz, 2004). The teeth of C. improcerus possess well developed anterior and posterior carinae as in C. bequaerti (Jouve and Schwarz, 2004), D phosphaticus (Jouve, 2005), D maghribensis (Jouve et al., 2006), and Hyposaurus derbianus (Cope, 1886), defining the labial and lingual surfaces. Unlike Congosaurus bequaerti (Jouve and Schwarz, 2004), Dyrosaurus (Jouve, 2005; Jouve et al., 2006), and Atlantosuchus coupatezi ( Jouve et al., 2008a), C. improcerus lacks noticeable striations on either face of t he teeth, but instead possesses apical lingual crenulations on the left m7 tooth. Chenanisuchus lateroculi was noted as having lacked striations on at least the labial surfaces (Jouve et al., 2005a), as in C. improcerus Hyposaurus rogersii has striations on the lingual surface (Denton et al., 1997) and Hyposaurus derbianus possesses longitudinal ridges on the lingual face and a smooth
51 condition on the exterior of its mandibular teeth (Cope, 1886). Arambourgisuchus khouribgaensis (Jouve et al., 2005b) was described as having a somewhat intermediate form of variably present and either absent or weak superficial striae. The teeth of Cerrjonisuchus improcerus do not curve distally, as in Dyrosaurus maghribensis (Jouve et al., 2006), Atlantosuchus coupatezi ( Jou ve et al., 2008a), Guarinisuchus munizi (Barbosa et al., 2008), and Phosphatosaurus gavialoides (Buffetaut, 1978a), nor are they slightly recurved as in Sokotosuchus ianwilsoni (Buffetaut, 1979) and Hyposaurus derbianus (Cope, 1886). The twisted carinae characteristic of Hyposaurus rogersii (Denton et al., 1997) was not noticed in any of the preserved teeth. P hylogenetic R elationships Five phylogenetic analyses at the genus level of Dyrosauridae have been published previously (Buffetaut, 1978a ; Jouve, 2005; Jouve et al., 2005b; Barbosa et al., 2008; Jouve et al., 2008a). Buffetaut ( 1978a ) included Phosphatosaurus Rhabdognathus Dyrosaurus and Hyposaurus in a manual cladogram. The most basal of which was Phosphatosaurus with Hyposaurus and Dyrosaurus bei ng more derived, and Rhabdognathus falling in between. Jouve (2005) conducted an analysis of 12 characters across five genera of Dyrosauridae. This analysis was expanded by Jouve et al. (2005b) to 30 characters and nine members of Dyrosauridae. Jouve et al (2008) further expanded this analysis to 43 characters and 11 species of Dyrosauridae. These studies found Sokotosuchus and Phosphatosaurus to be basal genera of the family, supporting the subfamily Phosphatosaurinae which at the time it was named includ ed only these two genera (Buffetaut, 1980). When Chenanisuchus was included, it was basal to all other members of Dyrosauridae (Jouve et al., 2005b; Jouve, 2008). Barbosa et al. (2008) modified the 30 characters of Jouve et al. (2005b) and added their new
52 taxon, Guarinisuchus munizi This study also found a basal placement of Chenanisuchus Sokotosuchus and Phosphatosaurus and placed Guarinisuchus as sister to a clade uniting Arambourgisuchus and Rhabdognathus New cranial specimens of Cerrejonisuchus improcerus allow for a reevaluation of the phylogenetic affinities of South American dyrosaurids. To help resolve the relationship of C. improcerus to other dyrosaurids, I performed a cladistic analysis of 82 cranial and mandibular characters (and one postcranial) for 13 dyrosaurid species and three outgroup taxa (Appendices A and B ). Early Cretaceous Sarcosuchus imperator (Sereno et al., 2001) and Elosuchus cherifiensis (de Lapparent de Broin, 2002) from Africa, and Late Cretaceous Terminonaris robusta (Wu et al., 2001) from North America were used as outgroup taxa. The cladistic analysis was rooted with Sarcosuchus imperator because it is the geologically oldest mesoeucrocodylian thought to be closely related to dyrosaurids but clearly not in the in group (Sereno et al., 2001; Jouve et al., 2005b), and because its cranium has been thoroughly described (Sereno et al., 2001). I included only members of Dyrosauridae known from at least somewhat complete cranial material in this analysis. The known dyrosaurid spec ies that were not included due to lack of cranial material are: the Cretaceous or Paleoceneaged Hyposaurus derbianus of Brazil (Cope, 1885, 1886), the Paleocene dyrosaurids Hyposaurus paucidens from Morocco (Arambourg, 1952; Jouve, 2007) and Congosaurus compressus from Mali (Jouve, 2007), and the Eocene dyrosaurid Rhabdognathus acutirostris from Tunisia (Buffetaut, 1978a ). All characters except 26, 29, 30, 32, and 53 (continuous, multistate characters; e.g., location of the posteriormost alveolus relative to the orbit/supratemporal fenestrae: character 30) were treated as unordered. Morphologic
53 data were compiled from the literature (Troxell, 1925; Buffetaut, 1978a and 1979; Buffetaut and Wouters, 1979; Denton et al., 1997; Sereno et al., 2001; Wu et al., 2001; Brochu et al., 2002; de Lapparent de Broin, 2002; Jouve and Schwarz, 2004; Jouve, 2005; Jouve et al., 2005a b; Jouve et al., 2006; Jouve, 2007; Barbosa et al., 2008; Jouve et al., 2008a) and study of specimens. While postcranial data are known for Dy rosauridae (Jouve et al., 2006; Schwarz et al., 2006), for the most part they have yet to be studied sufficiently for enough species to make them useful in this phylogenetic analysis Three characters were variable within species (character 5, lateral marg in of orbit; character 23, shape of maxillary margin; character 32, fusion of the nasals) and were coded as polymorphic. Characters not known for a taxon were coded as missing. Data were compiled in Mesquite version 2.5 (Maddison and Maddison, 2008) and th e cladistic analysis was done in PAUP version 4.0b10 (Swofford, 2003). A branch and bound search resulted in two most parsimonious cladograms (strict consensus presented in Fig. 9) with tree lengths of 170 steps, a consistency index of 0.547, a retention i ndex of 0.640, and a homoplasy index of 0.453. Our analysis corroborated the position of Chenanisuchus lateroculi at the base of Dyrosauridae, followed by Sokotosuchus ianwilsoni and Phosphatosaurus gavialoides Cerrejonisuchus improcerus gen. et sp. nov. placed relatively basally between P. gavialoides and Arambourgisuchus khouribgaensis C. lateroculi did not share a special relationship with the similarly short snouted C. improcerus as might have been expected based on snout proportions alone (Figs. 2 9, 2 10) Both species of Dyrosaurus and both species of Rhabdognathus paired in separate monophyletic clades, and a
54 polytomy occurred between Hyposaurus rogersii Congosaurus bequaerti and the clade uniting Rhabdognathus + Atlantosuchus coupatezi + Guarinis uchus munizi D iscussion Results from o ur study agree with previous placement of Chenanisuchus lateroculi Sokotosuchus ianwilsoni and Phosphatosaurus gavialoides as basal members of Dyrosauridae (Jouve, 2005; Jouve et al., 2005b; Barbosa et al., 2008; Jo uve et al., 2008a). The consensus cladogram presented here (Figs. 2 9, 2 10) is similar to that of Barbosa et al. (2008), only differing in a more basal position of Arambourgisuchus khouribgaensis relative to Hyposaurus rogersii and that instead corroborat es the results of Jouve et al. (2008). The polytomy at node 8 may be due to the relatively little cranial material known for Congosaurus bequaerti (known from only a skull missing all bones posterior to the orbits; coding for this taxon limited to 41% of t he characters in the matrix), this placement is tenuous and could change with discovery of more complete skulls. When C. bequaerti is removed, C. lateroculi still places as most basal, but the next node is a large polytomy containing S. ianwilsoni, P. gavi aloides Cerrejonisuchus improcerus H. rogersii and the clade uniting A. khouribgaensis Dyrosaurus Rhabdognathus Atlantosuchus coupatezi and Guarinisuchus munizi When all characters were treated as unordered, the analysis resulted in four equally mo st parsimonious cladograms reflecting four alternate relationships between H. rogersii the two Rhabdognathus species, A. coupatezi G. munizi and C. bequaerti However, the relationship of Cerrejonisuchus was not affected. As for previous analyses, our r esults support the monophyly of Rhabdognathus (Jouve et al., 2005b; Barbosa et al., 2008; Jouve et al., 2008a) united by frontal participation to the interfenestral bar of equal to or greater than onethird (character 38).
55 The Dyrosaurus clade is supported by three synapomorphies: a reversal to an ornamented interfenestral bar (character 8), T shaped interfenestral bar (character 9), and a posteriorly descending parietal laterosphenoid suture (character 63). Despite the lack of sufficient cranial material, species not included in the phylogenetic analysis have biogeographic relevance to the current study (Fig. 2 10). If Hyposaurus derbianus is at least considered a valid member of the genus Hyposaurus its presence in Brazil (Cope, 1886) implies a radiation of the genus Hyposaurus into the New World during the Late Cretaceous. Furthermore, the presence of Hyposaurus paucidens in Morocco, as well as other indeterminate Hyposaurus material (Jouve, 2007), implies a form of Hyposaurus remained in Africa into the Paleocene. Neither Congosaurus compressus nor Rhabdognathus acutirostris would imply drastically different paleobiogeography as both genera are already known from Africa (Jouve, 2007). The monophlyly of Dyrosauridae is supported by 12 unambiguous synapomor phies in the current study. Presence of all basal dyrosaurid taxa, together with two of three outgroups, in Africa strongly supports previous paleobiogeographic hypotheses for an African origin of Dyrosauridae (Jouve et al., 2005b; Jouve et al., 2008a). So uth American dyrosaurids are now known from the Paleocene of Bolivia, the Early Paleocene of Brazil, and the middle or late Paleocene of northeastern Colombia, as well as possibly from the Late Cretaceous in Bolivia and Brazil. The most complete material prior to this study is from the Pernambuco region of Brazil (Cope, 1885, 1886; Barbosa et al., 2008), Hyposaurus derbianus and G. munizi The genus Hyposaurus is
56 best known from Late Cretaceous and Paleocene deposits of eastern North America, all referred t o the species Hyposaurus rogersii (Denton et al., 1997). Hyposaurus is also known from much more fragmentary remains from the Paleogene of Africa (Jouve, 2007). Considering the temporal placement of the New World taxa (Fig. 2 10), three independent dispers als from Africa to the New World are suggested Presence of C. improcerus together with a number of undescribed taxa from the Paleocene of northeastern Colombia suggests there was a radiation of dyrosaurid crocodyliforms, possibly following the K P g boundary, in tropical South America. Barbosa et al. (2008) propose a dispersal from Africa to Brazil with continued immigration into North America. Our finding supports this dispersal route and adds to it evidence of coastal dyrosaurids in northern South America in Colombia, transitional between the Brazilian occurrence and North American occurrences. Also, presuming these crocodilians dispersed along coasts, this would also give a transitional location for the occurrence of dyrosaurids in South America between t he Brazilian specimens and the Bolivian specimens. In addition, C. improcerus has the shortest snout known within Dyrosauridae (Table 2 1). The next shortest snout within Dyrosauridae belongs to C. lateroculi from the Paleocene of Morocco (Jouve et al., 2005a). Separation of C. improcerus and C. lateroculi within the phylogenetic analysis (Figs. 2 9, 2 10) suggests that the short snouted condition evolved at least twice within Dyrosauridae. The short snouted condition most likely evolved to adapt to a more generalized diet, still including fish but invertebrates and small vertebrates as well, as opposed to the presumed strongly piscivorous diet of the typical long snouted dyrosaurids (Buffetaut, 1979; Denton et al.,
57 1997) The morphological similarities betw een the two short snouted species are fairly limited beyond their snout proportions The interfenestral bar for both species is relatively wide and squareshaped in cross section In addition, the posterior margin is relatively transversally straight in bo th short snouted species. In long snouted species the margin can be either straight (e.g. Dyrosaurus ) or indented (e.g. Rhabdognathus ). The most noteworthy differences are their relative orbital placement and development of the occipital tuberosities. Rega rding ontogeny, all cranial sutures seem to be fully fused with the only possible exception being the nasal of UF/IGM 32. The partially fused nasal of UF/IGM 32 indicates this individual was slightly less mature than UF/IGM 29 or 31, particularly consideri ng its smaller size (Fig. 2 7). Moreover, the associated postcrania of UF/IGM 31 further indicate morphologically mature status (Fig. 2 11). In crocodilians, the neurocentral sutures close from tail to neck during ontogeny (Brochu, 1996), implying that the closed neurocentral sutures of the anterior dorsal vertebrae of C. improcerus UF/IGM 31, indicate a morphologically mature individual (Fig. 2 11). Furthermore, no isolated centra were associated with this partial skeleton. Further evidence of maturity co mes from the preserved osteoderms. Osteoderms in Alligator begin calcification around one year into their growth period as a small round nucleus which then grows during life to articulate with other osteoderms and provide the dermal shield (Vickaryous and Hall, 2008). Assuming similar developmental mechanisms governed dyrosaurid osteoderm growth, these osteoderms likely represent an individual that has reached morphological maturity. Due to the similar size between the holotype (UF/IGM 29) and the referred UF/IGM 31 and fully fused cranial sutures, these both likely represent
58 morphologically mature specimens and the characters that distinguish C. improcerus from other dyrosaurid species likely reflect unique taxonomic features as opposed to the features of y ounger stages in a known dyrosaurid species. Thus, several features including snout proportion and supratemproal fenestrae shape and orientation are considered to be morphologically distinct characters from other members of Dyrosauridae. Until further spec imens are discovered, the estimated upper size limit of the species based on the largest specimen (2.22 m; UF/IGM 31; Table 2 1), which is similar to, but still smaller than, the lower size limit of 2.48 m for next smalled dyrosaurid, Hyposaurus rogersii Following Sereno et al. (2001), the body size of C. improcerus was approximated based on dorsal skull length of the morphologically mature specimens UF/IGM 29 and 31 (UF/IGM 32 is too incomplete for an accurate estimate, and likely morphologically immature ). Using the known relationship between these measurements for Gavialis gangeticus and Crocodylus porosus the total body length of morphologically mature C. improcerus was likely bet ween 1.22 and 2.22 m (Table 2 1). As compared to other estimates of dyros aurid length by Jouve et al. (2005a), C. improcerus has the shortest total body length in the family (Table 2 1). The longest dyrosaurid from this study was Phosphatosaurus gavialoides at 7.22 8.05 m Therefore the new body length range for mature dyrosaur ids is between 1.22 m and 8.05 m.
59 Table 21. Snout proportions of all members of Dyrosauridae with material complete enough for skull length estimation. Notably absent are Rhabdognathus aslerensis which lacks most of the front of the snout needed to estim ate dorsal skull length as well as preorbital skull length. Congosaurus bequaerti is only known from the anterior portion of the skull (Jouve and Schwarz, 2004); however, dorsal skull length and body length were estimated by Jouve et al. (2008). Abbreviati ons: DL, dorsal skull length; PreoL, preorbital skull length; R, ratio of preorbital skull length to dorsal skull length; TBL, estimated total body length using method by Sereno et al. (2001). Citations are marked by numbered superscripts: 1Jouve et al., 2005a; 2an estimation from Jouve et al., 2008a; 3an estimation from figure in Barbosa et al., 2008; 4Jouve et al., 2005b; 5Jouve et al., 2006; 6Jouve et al., 2008a. DL (cm) PreoL (cm) R (PreoL/DL) x 100 TBL (m) Cerrejonisuchus improcerus (UF/IGM 31) 31.4 17.2 54.78 1.72 2.22 Cerrejonisuchus improcerus (UF/IGM 29) 25.8 15.3 59.30 1.22 1.79 Chenanisuchus lateroculi 1 57.6 36.5 63.37 3.57 4.24 Congosaurus bequaerti 2 63 41 65.08 3.97 4.66 Guarinisuchus munizi 3 47.1 30.8 65.41 2.79 3.43 Hyposaurus rogers ii 1 42.9 28.2 65.73 2.48 3.11 Sokotosuchus ianwilsoni 1 60.1 39.7 66.06 3.75 4.44 Phosphatosaurus gavialoides 1 107 72 67.29 7.22 8.05 Arambourgisuchus khouribgaensis 4 100 71.5 71.50 6.71 7.51 Dyrosaurus phosphaticus 1 104 75 72.12 7.00 7.82 Dyrosau rus maghribensis 5 89 97 73.00 5.89 7.28 Rhabdognathus keiniensis 1 73.1 53.4 73.05 4.72 5.44 Atlantosuchus coupatezi 6 104.5 83 79.43 7.04 7.86
60 Table 22. Alveolus dimensions and spacing for the upper dentition of the holotype, UF/IGM 29, and the l ower dentition of the referred mandible, UF/IGM 30. Alveolus width measured transversally at anteroposterior midpoint Alveolus length measured transversally at anteroposterior midpoint. Width between left and right alveoli measured from left medial anteroposterior midpoint to the right medial anteroposterior midpoint Interalveolar length measured from posterior transverse midpoint to anterior transverse midpoint of adjacent alveolus. Dashes are used when preservation is not sufficient for measurement. All measurements in mm. Upper d entition Alveolus p osition pm1 pm2 pm3 pm4 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 Left a lveolus w idth 4 81 5 59 6 36 4 80 3 38 9 71 2 76 6 06 6 75 5 58 5 59 2 36 4 56 Right a lveolus w idth 5 89 4 80 10 21 1 91 6 82 4 39 9 25 2 13 4 78 5 47 6 92 10 34 5 28 Left a lveolus l ength 7 00 5 80 10 90 6 31 6 54 10 06 4 85 8 58 8 75 6 96 5 35 6 93 5 60 Right a veolus l ength 6 89 5 24 8 35 2 34 4 05 4 09 8 74 3 10 6 61 7 01 9 83 9 40 5 71 Width between l eft and r ight alveoli 1 91 26. 39 25. 99 23. 71 21. 19 23. 51 32. 46 38. 44 44. 56 52. 67 67. 32 Interalveolar p osition pm1 2 pm2 3 pm3 4 pm4 m1 m1 2 m2 3 m3 4 m4 5 m5 6 m6 7 m7 8 m8 9 m9 10 m10 11 Left i nteralveolar l ength 15 78 11 17 10 09 12 51 8 09 7 91 7 13 6 50 6 75 4 51 Right i nteralveolar l ength 11 34 11 97 10 80 17 16 12 08 13 82 7 58 14 33 7 09 6 38 3 19 3 4 Lower d entition Alveolus p osition d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12 d13 Left a lveolus w idth 2 35 4 12 4 80 7 10 2 67 3 42 4 17 4 20 Right a lveolus w idth 5 49 3 91 5 06 2 04 4 32 4 11 3 54 Left a lveolus l ength 1 78 6 90 4 49 8 03 3 31 2 84 3 94 5 07 3 52 Right a lveolus l ength 2 82 3 37 8 76 2 83 4 83 4 62 4 23 Width between l eft and r ight alveoli 11. 16 15. 98 12. 82 14. 90 17. 17 33. 56 40. 53 Interalveolar p osition d1 2 d2 3 d3 4 d4 5 d5 6 d6 7 d7 8 d8 9 d9 10 d10 11 d11 12 d12 13 Left i nteralveolar l ength 5 51 3 48 3 38 8 37 7 94 5 57 3 94 Right i nteralveolar l ength 3 87 12 00 3 88 5 31 3 92
61 F igure 2 1. World map of locations of known crocodyliform fossil material during the Paleocene. Circles represent locations ascertained as Paleocene in age, squares represent locations which have been contested as possibly Late Cretaceous in age, and the star represents the new locality in northeastern Colombia. Map of the Paleocene by Scotese ( 2001)
62 F igure 22. Location and stratigraphic column from which the new fossil material was discovered. A ) stratigraphic column including the layer which yielded the fossils herein described, marked by an arrow. B ) map of Colombia, star marks location of the field site from which crocodyliform fossils were recovered.
63 F igure 2 3. S kull of Cerrejinosuchus improcerus UF/IGM 29, from the Cerrejn coal mine of northeastern Colombia, middle late Paleocene, in dorsal view. A ) photograph; B ) sketch. Abbreviations: bo basioccipital; en external nares; eo, exoccipital; f, frontal; ifb, interfenestral bar; j, jugal; l, lacrimal; lsp, laterosphenoid; m, maxilla; n, nasal; or, orbit; ot, occipital tuberosity; p, parietal; pm3, third premaxillary tooth; pm, premaxilla; po, postorbital; prf, prefrontal; prp, paroccipital process; q, quadrate; s q, squamosal; stf, supratemporal fenestra; vt, ventral tubercle. Scale bar equals 10 cm.
64 F igure 2 4. Skull of Cerrejinosuchus improcerus UF/IGM 29, from the Cerrejn coal mine of northeastern Colombia, middle late Paleocene. A ) UF/IGM 29 in lateral vi ew; B ) UF/IGM 29 in occipital view; C ) UF/IGM 29 sketch of occipital view. Abbreviations: bo, basioccipital; car, carotid foramen; eo, exoccipital; fm, foramen magnum; fv, foramen vagi; oc, occipital condyle; ot, occipital tuberosity; p, parietal; prp paroccipital process; ptf, posttemporal fenestra; q, quadrate; so, supraocciptal; sq, squamosal. Both scale bars equal 10 cm.
65 F igure 2 5. Skull of Cerrejonisuchus improcerus UF/IGM 29, from the Cerrejn coal mine of northeastern Colombia, middle late Paleocene, in ventral view. A ) photograph; B ) sketch. Abbreviations: bo, basioccipital; bsp, basisphenoid; car, carotid foramen; eo, exoccipital; fv, foramen vagi; if, incisive foramen; j, jugal; m, maxilla; m6 8, sixth through eighth left maxillary teeth; mef, medial eustachian foramen; pm3, third premaxillary tooth; pal, palatine; pm, premaxillary; q, quadrate; sof, suborbital fenestra. Scale bar equals 10 cm
66 F igure 2 6. Referred skull of Cerrejonisuchus improcerus UF/IGM 31, from the Cerrejn coal mine o f northeastern Colombia, middle late Paleocene, in dorsal view. A ) UF/IGM 31 photograph; B ) UF/IGM 31 sketch. Abbreviations: bo, basioccipital; en, external nares; eo, exoccipital; f, frontal; if, incisive foramen; ifb, interfenestral bar; itf, infratempor al foramen; j, jugal; l, lacrimal; m, maxilla; n, nasal; or, orbit; ot, occipital tuberosity; p, parietal; pm3, third premaxillary tooth; pm, premaxilla; po, postorbital; prf, prefrontal; prp, paroccipital process; q, quadrate; qj, quadratojugal; sq, squam osal; stf, supratemporal fenestra; vert, vertebra vt, ventral tubercle. Dotted lines represent sutures which were not clear. Specimen has a partial thoracic vertebra fused to the ventral side of the skull as a result of deformation, visible also in dorsal view. Scale bar equals 10 cm.
67 F igure 2 7. Referred snout of Cerrejonisuchus improcerus UF/IGM 32, from the Cerrejn coal mine of northeastern Colombia, middle late Paleocene. A ) UF/IGM 32 in dorsal view; B ) UF/IGM 32 in ventral view. Scale bar equals 5 cm.
68 F igure 2 8. Referred mandible of Cerrejonisuchus improcerus UF/IGM 30, from the Cerrejn coal mine of northeastern Colombia, middle late Paleocene, in dorsal view. A ) UF/IGM 30 photograph; B ) UF/IGM 30 sketch. Abbreviations: d, dentary; d113, den tary alveoli; dat, disassociated teeth; sp, splenial. Scale bar equals 10 cm.
69 F igure 29. Results from phylogenetic analysis of 82 characters and 14 taxa ( Appendices A and B ). Single mos t parsimonious cladogram of branch and bound search using both ordered and unordered characters. Tree Lengths: 170 each; C.I.: 0.547; R.I.: 0.642; R.C.: 0.351; H.I.: 0.453. Unambiguous synapomorphies, with a superscript R indicating instances of reversal: Node 1, 1(1), 3(1), 6(1), 11(1), 15(1), 19(1), 27(1), 50(1), 52(1), 55(1), 60(1), 75(1); Node 2, 7(1), 8(1), 74(1); Node 3, 10(1), 32(2); Node 4, 31(1), 80(1); Node 5, 9(2), 22(1), 33(0)R; Node 7, 8(0)R, 9(1), 63(1); Node 8, 42(1), 50(2), 59(1), 81(1), 82(1); Node 9, 46(1), 48(1); Node 10, 39(1); Node 11, 5(0)R.
70 F igure 2 10. Phylogenetic relationship placed in stratigraphic and paleobiogeographic context. Dat es from Gradstein et al., 2004.
71 F igure 2 11. Associated postcrania of UF/IGM 31. A B ) anterior dorsal vertebra (likely the third or fourth position); A ) in cranial view; B ) in right oblique view of ventral aspect showing fusion of neurocentral suture; C ) lateral osteoderm. Abbreviations: hyp, hypapophysis; ncs, neurocentral suture; ns, neural spine; poz, postzygapophysis; tp, transverse process Scale bar equals 5 cm.
72 CHAPTER 3 A NEW LONGIROSTRINE DYROSAURID (CROCODYLOMORPHA, MESOEUCROCODYLIA) FROM THE PALEOCENE OF NORTHEASTERN COLOMBIA: BIOGEOGRAPHIC AND BEHAVIOURAL IMPLICATIONS FOR NEW WORLD DYROSAURIDAE I ntroduction The Cerrej n Formation in northeastern Colo mbia ( Fig. 3 1) has been estimated to be middle late Paleocene based on carbon isotopes, pollen and spores (Jaramillo et al. 2007) and has yielded the first good evidence of tropical terrestrial ecosystems of that age in South America1. Recent discoveries, all from exposures in the Cerrej n coal mine, include the oldest megafossil evidence of neotropical rainforests (Doria et al. 2008; Herrera et al. 2008; Gomez Navarro et al. 2009; Wing et al. 2009), many vertebrae and ribs of the largest known snake Titan oboa cerrejonensis (Head et al. 2009), large pleurodire turtles (Cadena et al. 2010), multiple species of undescribed dipnoan and elopomorph fishes (Bloch et al. 2005), and a new short snouted dyrosaurid crocodyliform Cerrejonisuchus improcerus (Hastings a nd Bloch 2007; Hastings et al. 2010). The first vertebrate fossils to be recovered from the Cerrej n Formation, a partial mandible and associated postcrania, were discovered and collected in 1994 by Mr Henry Garcia, a coal geologist working in the Cerrej n coal mine who was monitoring field operations on the south face of the Expanded West Pit. Mr Garcia retrieved the fossils from just below Coal Seam 40 ( Fig 3 1) after seeing them exposed by one of the large earth movers. The fossils were subsequently deposited in a display case at the 1 Reprinted with permission fr om Hastings, A. K., Bloch, J. I., Jaramillo, C.A. 2011. A new longirostrine dyrosaurid (crocodylomorpha, mesoeucrocodylia) from the paleocene of northeastern colombia: biogeographic and behavioural implications for new world dyrosauridae. Palaeontology 54: 1095 1116
73 mine geology offices until they were identified as a dyrosaurid a decade later. Based on these specimens and others recovered by Florida Museum of Natural History Smithsonian Tropical Research Institute (FLMNH STRI) collecting expeditions from 2004 through 2007, here is described a second new species of dyrosaurid from the Cerrej n Formation. To date, fossils attributed to the new species have been recovered from underclays below three distinct coal seams within the Cerrej n Formation ( F ig. 3 1). As such, it is the only crocodyliform taxon yet discovered to transcend more than one horizon within the Cerrej n Formation. The fossils were recovered from sediments that were deposited prior to the warming trend of the Paleocene Eocene Thermal Maximum (Jaramillo et al. 2010), although temperatures were still much warmer than today (Head et al. 2009). Dyrosauridae is a diverse family of mesoeucrocodylians that likely had its origins in the Late Cretaceous, survived the K P g boundary extinction event, and is last known from the Late Eocene (Brochu et al. 2002). Dyrosaurid fossils have been recovered from transitional freshwater marine sediments through this interval in Africa, Asia, Europe, North America and South America. The publi shed South American record of dyrosaurids is restricted to six localities, all Late Cretaceous or Paleocene in age (Cope 1886; Langston 1965; Argollo et al. 1987; Marshall and de Muizon 1988; Gasparini 1996; de Carvalho and de Azevedo 1997; Gallo et al. 2001; Barbosa et al. 2008; Hastings et al. 2010), and is very fragmentary. The best known taxa are both from the Paleocene: Guarinisuchus munizi from Brazil (Barbosa et al. 2008) and C errejonisuchus improcerus (Hastings et al 2010) from the Cerrejn Formati on. These taxa are distinctly different from one another, with G. munizi having a substantially longer snout than that of C. improcerus While shorter than that of Old World
74 dyrosaurids, the longirostrine condition of G. munizi seems to be shared with Hypo saurus derbianus from the Paleocene of Brazil, known from a nearly complete dentary, and likely represents the primitive condition for New World Dyrosauridae. The new species described here represents the third named longirostrine dyrosaurid from the Paleocene of South America. Fossils of the new taxon (Hastings and Bloch 2008) are catalogued at both the Museo Geol gico, at the Instituto Nacional de Investigaciones en Geociencias, Miner a y Quimica (IGM) in Bogot Colombia and the Florida Museum of Natural History (FLMNH), and are currently housed at the FLMNH. Fossils of the new taxon were recovered from sediments deposited in a large fluvial depositional setting, pertaining to the ancient Amazonian basin (Hoorn et al. 2010). The postcrania indicate that w hile the new taxon was generally similar to Old World Dyrosaurus in its swimming mode, it is distinctly different in ways that likely reflect a difference in habitat utilization in this new dyrosaurid. Institutional A bbreviations AMNH, American Museum of Natural History; GSP, Geological Survey of Pakistan; IGM, Museo Geol gico, at the Instituto Nacional de Investigaciones en Geociencias, Miner a y Quimica, Bogot Colombia; OCP DEK GE, Office Ch rifien des Phosphates, Direction de lExploitation de Khouribga, Geologie Exploitation, Khouribga, Morocco; SMNKPAL, Staatliches Museum f r Naturkunde Karlsruhe; STRI, Smithsonian Tropical Research Institute; UF, Florida Museum of Natural History (FLMNH), University of Florida; USGS SAP, United States Geological Sur veySaudi Arabian collection; YPM, Yale Peabody Museum.
75 Terminology and A natomical A bbreviations Following the study by Hastings et al. (2010), teeth and alveoli of the dentary (d) are referred to by a sequential numbering system, with d1 being the most anterior. Systematic Paleontology C rocodylomorpha, Walker, 1970 C rocodyliformes Hay, 1930 M esoeucrocodylia, Whetstone and Wybrow, 1983 D yrosauridae, de Stefano, 1903 A cherontisuchus G en. N ov. Derivation of name Acheron, from ancient Greek mythology, the river Acheron (the river of woe) a branch of the underworld river Styx over which Charon ferried the dead across into Hades; suchus, Greek for crocodile. Type species. Acherontisuchus guajiraensis Range Middle Late Paleocene, Colombia. Diagnosis As f or the type species. Acherontisuchus guajiraensis, S p. N ov. Derivation of name. Named for the Guajira Peninsula in northeastern Colombia, the location of the Cerrej n Coal mine from which all specimens described here were recovered. Holotype. UF IGM 34, a mostly complete mandible including left and right dentaries, splenials, 14 partial mandibular teeth, right surangular, and four maxillary fragments, four partial teeth, and two partial ribs.
76 Type locality. All known specimens are from the Cerrej n Format ion within the Cerrej n Coal Mine (11o08.944 N, 72o32.891 W) in northeastern Colombia. Middle to late Paleocene in age. Type stratum. The type stratum is below Coal Seam 85 within t he La Puente Pit. Referred specimens. UF IGM 35, mandible including left and right dentaries and splenials, the left surangular, angular and articular, and a total of three partial teeth. Associated postcrania include two ribs, one sacral vertebra with partial sacral ribs and one metatarsal. Th ese fossils were recovered from the underclay of Coal Seam 90 within the La Puente Pit (11o09 03.70 N, 72o33 18.98 W). UF IGM 36, edentulous mandible including partial left and right dentaries, recovered from the underclay of Coal Seam 40 within the West Extension Pit. Also recovered were a dorsal vertebra (UF IGM 37), a nearly complete ilium and ischium (UF IGM 38), and a femur (UF IGM 39) from the same locality, all of which might be associated and are here referred to one or more individuals of A. guajiraensis Diagnosis. A longirostrine dyrosaurid that differs from all other dyrosaurids by the following unique combination of characteristics: (1) 19 22 mandibular teeth; (2) a symphysis that ends between 17th and 19th alveoli; (3) splenials that end anteriorly between 10th and 13th alveoli; and (4) maxillae that have straight lateral margins and are weakly ornamented. Remarks. It differs from: (1) Dyrosaurus Atlantosuchus Rhabdognathus and Congosaurus in having a shorter snout; (2) Arambourgisuchus in having strongly striated lingual and buccal surfaces of teeth; (3) Chenanisuchus in possessing teeth that are not strongly laterally compressed, some of which possess striations; (4)
77 Rhabdognathus in having a mandible that is much wider than high and a mandibular symphysis which ends prior to 19th mandibular alveolus; (5) Congosaurus in having a shorter snout that is wider than high; (6) Guarinisuchus in having a much larger inferred total body length; (7) Sokotosuchus and Phosphatosaurus in having smooth margined maxillae; (8) Hyposaurus in having a mandibular symphysis that is much wider than tall; and (9) Cerrejonisuchus in having greater body size, a greater overall number of mandibular teeth, and a proportionally greater number of symphyseal tee th. Description General. While a complete skull of Acherontisuchus guajiraensis has not been recovered, its estimate d total length is 72 86 cm, based on the morphology and measurements of the mandible. The skull length estimate, from the presumed tip of th e snout to the occipital condyle, includes a range of possibilities for the extent of the occipital condyle and the premaxilla. The quadratearticular surangular articulation corresponds to the approximate position along the skull length of the occipital condyle in Dyrosaurus maghribensis (Jouve et al. 2006), and is used here as a reference for estimating skull length in A. guajiraensis The anterior extent of the skull was further estimated based on alveolar size and spacing of the anterior mandibular sy mphysis. All three fossils (UF IGM 34 36) preserve morphology consistent with the interpretation that A. guajiraensis had a long and narrow snout that would have represented 56 65 per cent of the estimated total skull length (Table 3 1). As the estimate incorporates large allowances f or variation, I am very confident that this species had snout proportions within this range. Maxilla. The holotype of A. guajiraensis includes four associated fragments of the right and left maxilla ( Fig 3 2). The preserved mediodorsal margin of these
78 fra gments suggests that the maxillae would have been separated by the nasals, which were not recovered in this specimen. While the recovered sections of the maxillae contain no less than four partial teeth, relative tooth positions are not preserved and cannot be estimated with confidence. Based on comparison to the mandible, most of the maxillae must be present, with only the portions connecting the different sections missing. The more complete right side possesses a total of 11 preserved alveoli ( F ig. 3 2). As portions are missing, this implies that the maxillary tooth count for A. guajiraensis is greater than 11. The maxilla is very weakly ornamented dorsally and has a smooth, straight lateral margin ( F ig. 3 2). Mandible. Despite imperfect preservation, the fossils lack visible signs of significant deformation and likely represent similar proportions as found in life, particularly for the holotype ( F ig. 3 3). The width of the symphyseal region of the dentaries splenials is wider than its height throughout it s length. UF IGM 34 possesses 19 alveoli ( F ig. 3 3), while UF IGM 35 possesses 22 ( F ig. 3 4). UF IGM 36 is incomplete, but possesses 8 alveoli ( F ig. 3 5). The seventh alveolus is reduced relative to the eighth and is placed notably closer to the eighth than the sixth in both UF IGM 34 and 35. The symphysis ends posteriorly at the 17th alveolus in UF IGM 34 and between the 18th and 19th alveoli in UF IGM 35. The alveoli of the symphysis are wider and rounder than those posterior to the symphysis. The postsymphyseal alveoli are reduced in size, and their medial borders are formed by the splenial. A series of depressions adjacent to the alveoli is evident on the left side of the mandible of UF IGM 35. These depressions are likely for occlusion wit h maxillary teeth, and are smaller
79 and shallower than the alveoli that house the mandibular teeth. A prong of the dentary extends posteriorly into the surangular, dorsal to the mandibular fenestra. The splenials in both UF IGM 34 and 35 form sharp wedges that participate broadly in the symphysis. The splenials end anteriorly between the 10th and 11th alveoli in UF IGM 34 on the dorsal surface and even with the 13th alveolus on the ventral surface ( F ig. 3 3). The splenials in UF IGM 35 end anteriorly b etween the 12th and 13th alveoli on the dorsal surface ( F ig. 3 4) and their anterior extent cannot be discerned on the ventral surface. The spreading angle of the splenials, as measured from the anterior point along the left and right dentary splenial sutu res, is 17.5 degrees in UF IGM 34 and 33.5 degrees in UF IGM 35. However, when measured from the posterior symphysis of the splenials along the medial dorsal surface, the angle is 57.9 degrees for UF IGM 34 and 58.5 degrees in UF IGM 35. The splenials cannot be discerned in either dorsal or ventral views of UF IGM 36 ( F ig. 3 5). The angular joins with the dentary ventral to the external mandibular fenestra and contributes broadly to the ventral portion of the back of the mandible. While the preservation of the retroarticular process is incomplete, the angular clearly participates in at least the ventral portion of its base ( F ig. 3 6). The surangular reaches anteriorly nearly to the level of the posteriormost alveolus ( F ig. 3 6). The retroarticular processes of both UF IGM 34 and 35 are incomplete, but clearly are formed in large part by the surangular. The surangular contributes to the lateral portion of the glenoid fossa. The surangular of the holotype, UF IGM 34, bears a foramen aerum on the lateral side ( F ig. 3 3). The foramen is fully contained within this bone and is just caudal to a transversely oriented rugosity. A small,
80 narrow shelf arises from this rugosity and extends anteroposteriorly along the lateral surface of the surangular and narrows posteriorly, forming part of the base of the retroarticular process. The surangular of UF IGM 35 bears a ridge that extends anteroposteriorly and defines the boundary between the dorsal and lateral surfaces of the bone ( F ig. 3 6). The articular forms the medial portion of the glenoid fossa. Posterior to the fossa is a depression, forming a shelf that extends anteroposteriorly along the preserved retroarticular process ( F ig. 3 6). If undistorted, this shelf gives the cross section of the retroarticular process an Lshape. The articular forms the medial portion of the retroarticular process. Onl y the anterior portion of the left external mandibular fenestra is preserved in UF IGM 35. The fenestra appears small and is bordered anteriorly and ventrally by the dentary, dorsally by the surangular, and posteriorly by the angular ( F ig. 3 4). Dentition. The symphyseal teeth have wide bases that narrow towards their apex. A distinct carina is present on the preserved teeth, and most have preserved striations along both lingual and labial surfaces ( F ig. 3 7). The carinae are well developed and define the labial and lingual surfaces of the tooth. The anterior carina is not fully preserv ed on any tooth, but the preserved portion does not indicate any twisting. Postsymphyseal alveoli are only slightly lateromedially compressed, but are notably smaller in all dimensions than the symphyseal alveoli ( F ig s. 3 3, 3 4). Dorsal vertebra. A single dorsal vertebra (UF IGM 37) was found near UF IGM 36 and is here referred to A. guajiraensis The anterior articular facet of the centrum bears a circular tubercle at its lower right centre ( F ig. 3 8). The vertebra is a posterior dorsal, based on its lack of any hint of hypapophysis and its squareshaped
81 anterior posterior articular facets, most likely between positions 8 and 13 ( F ig. 3 8). However, as only partial transverse processes were preserved, it is difficult to assign an exact position withi n the vertebral column. In ventral and dorsal views, the centrum of the vertebra is distinctly hourglass shaped. In ventral view, the width of the central constriction (32 mm) is 64 per cent of the caudal margin (50 mm). In lateral view, the centrum height (41 mm) is 71 per cent of the centrum length (58 mm). Also in lateral view, the centrum length at the ventral margin (56 mm) is 3 per cent shorter than at the level of the neurocentral suture (58 mm). Sacrum. A second sacral vertebra with partial left and right second sacral ribs was found associated with UF IGM 35 ( F ig. 3 9). The vertebra can be identified as the second sacral based on the lack of a tuber on the anterior surface of the centrum as well as the articulation of the sacral rib exclusively wi th the centrum with no facet for additional articulation with a more anterior vertebra. The second sacral ribs were identified as such based on the identification of the vertebra as well as their complete lateral circumferential suture with the lateral ver tebral surface. The second sacral ribs insertion onto the second sacral vertebra occupies nearly the entire lateral surface, very different from the transverse process of a dorsal vertebra, which is more limited. Ilium. A pelvis, UF IGM 38, was collected with UF IGM 36 and is thus attributed to A. guajiraensis The iliac blade is large, with a convex dorsal margin, rounded posterior margin and a strongly concave anterior margin ( F ig. 3 10). The iliac craniodorsal tubercle is very pointed and projects strongly anterodorsally. The ventral margin bears peduncles anteriorly and ventrally for articulation with the ischium. The anterior peduncle is incomplete. The acetabular foramen created by the ilium and
82 ischium is small and longer dorsoventrally than it is anteroposteriorly. The supracetabular crest extends along the lateral surface from the iliac craniodorsal tubercle ventrally threefourths of the distance to the ventral margin of the ilium. Articular surfaces for the first and second sacral ribs are preserved on the medial surface, but their overall shapes cannot be reliably discerned ( F ig. 3 10). Ischium. The ischium of UF IGM 38 is long and notably curved posteriorly with a straight shaft ( F ig. 3 10). The connection between the i schium and ilium is complete posteriorly and incomplete anteriorly. Although the articular surface for the pubis is not completely preserved, it appears to have been oriented at approximately 90 degrees from the shaft of the ischium. What is preserved of t he ventral surface of the ischium shows no indication of expansion and instead smooths to a point. The preserved portion of the anterior surface thins significantly indicating termination near the anteromost preserved surface. The anterior surface is compl ete up until a severe restriction ( F ig. 3 10) at which point there is minimal missing material as the bone thins significantly. The ischiac blade is long, smooth, thin and lacks any notable rugosities. Ribs. Two rib fragments were associated with UF IGM 34 ( F ig. 3 7), and two fairly complete ribs were associated with UF IGM 35 ( F ig. 3 9). The most complete rib from UF IGM 35, a mid thoracic, clearly shows the vertical orientation typical of dyrosaurids (Schwarz Wings et al. 2009) and bears a median cr est along its lateral surface. The ribs are otherwise flat and smooth. Femur. A femur (UF IGM 39) was collected with UF IGM 36 and is assigned to A. guajiraensis The femur is sigmoidally curved with a straight shaft ( F ig. 3 11). Relative to the midlin e of the shaft, the proximal end is angled medially 52 degrees and
83 the distal end is angled laterally 51 degrees. The fourth trochanter is enlarged and clearly visible in cranial view, despite flattening, and is located along the border of the cranial and lateral surface. A shallow ovular depression forms the paratrochanteric fossa, anterior to the fourth trochanter. The lateral and medial condyles of the distal extremity are separated by an intercondylar fossa ( F ig. 3 11). Metatarsal. A single metatarsal w as associated with UF IGM 35 ( F ig. 3 9). The metatarsal is lacking its distal end, but possesses the midshaft and proximal portions. The proximal surface is spatulate and becomes progressively thinner towards the proximal most edge. The proximal articular surface is largely worn away, but still preserves an elongate form ( F ig. 3 9). There is a strong proximodistal groove along the dorsal surface, to one side of the midline. A strong crest forms near the proximal end of the metatarsal, which flares along t he edge towards the proximal most edge of the bone. Towards the distal end, a slight constriction occurs for the distal head of the metatarsal, which has been collapsed atop the plantar surface. Comparison General. The snout proportions for UF IGM 34 and 35 were estimated based on minimum and maximum likely skull lengths, resulting in a range of 56 65 per cent for the proportion of the skull composed of the snout (Table 3 1). The estimated snout proportions of Acherontisuchus guajiraensis impl y a longirostrine form, unlike the relatively short snouted condition seen in the other dyrosaurid from this locality, Cerrejonisuchus improcerus (Hastings et al. 2010). Nevertheless, the snout of A. guajiraensis is shorter than such long snouted dyrosauri ds as Dyrosaurus (Jouve et al. 2006), Rhabdognathus (Jouve 2007) and Atlantosuchus (Jouve et al. 2008a). The snout
84 shape of Acherontisuchus is similar in basic structure to dyrosaurids included in the skull shape study conducted by Pierce et al. (2009). M axilla. The maxilla of A. guajiraensis is straight and not festooned as it is in Phosphatosaurus (Buffetaut 1978a) and Sokotosuchus (Buffetaut 1979a). The dorsal surface of the maxilla of A. guajiraensis is very weakly ornamented, in contrast to that of the shallow longitudinal and spaced furrows of Dyrosaurus maghribensis (Jouve et al. 2006) or the dorsal and lateral ornamentation of C. improcerus (Hastings et al. 2010). The maxillary tooth count (greater than 11) of A. guajiraensis is greater than the t otal tooth count (11) known for skulls of C. improcerus (Hastings et al. 2010). M andible. The total number of mandibular teeth for A. guajiraensis (19 22) is much higher than that of C. improcerus (13; Hastings et al. 2010). The number of symphyseal teeth for A. guajiraensis (17 19) is similar to that of D. maghribensis (17 21; Jouve et al. 2006) but greater than that of C. improcerus (9; Hastings et al. 2010) and that of Hyposaurus derbianus (12; pers. obs.). The disparity of alveolar size between d7 and d8 of A. guajiraensis is much greater than that of C. improcerus (Hastings et al. 2010). The anterior extent of the splenials of A. guajiraensis ranges from between d10 and d11 and between d12 and d13, which is more posterior than the condition seen in C. improcerus (between d6 and d7; Hastings et al. 2010), Hyposaurus rogersii (d7; Jouve 2007), or H. derbianus (d9; pers. obs.). A. guajiraensis is instead more similar in this respect to Arambourgisuchus khouribgaensis (between d10 and d11; Jouve et al. 2005b ) and D. maghribensis (d11 d14; Jouve et al. 2006). The symphysis is much wider than high, as measured from the uncompressed holotype (UF IGM 34), wider than in Hyposaurus Congosaurus or Rhabdognathus ( Fig. 3 12).
85 The lateral placement of the foramen aerum seen in A. guajiraensis has been noted in Congosaurus bequaerti (Jouve and Schwarz 2004) and D. maghribensis (Jouve et al. 2006), but differs from the foramens medial placement in extant crocodilians (Iordansky 1973). In extant crocodilians, the foramen allows for a siphonium to connect the internal cavity of the quadrate to the cavity of the articular (Iordansky 1973). Therefore, in dyrosaurids, this cavity in the mandible must instead be located within the surangular. The external mandibular fenestr a of A. guajiraensis differs from that of D. maghribensis in being bound ventrally by the dentary, not the angular and dentary (Jouve et al. 2006), or angular only as it is in C. bequaerti (Jouve and Schwarz 2004). Dentition. The rounded apices of the teet h of A. guajiraensis are comparable to those of C. improcerus (Hastings et al. 2010) and C. bequaerti (Jouve and Schwarz 2004). As in C. bequaerti (Jouve and Schwarz 2004), Dyrosaurus phosphaticus (Jouve 2005), D. maghribensis (Jouve et al. 2006), C. impro cerus (Hastings et al. 2010) and H. derbianus (Cope 1886), the carinae of A. guajiraensis are well developed and define the lingual and labial surfaces of the teeth. Like C. bequaerti (Jouve and Schwarz 2004), Dyrosaurus (Jouve et al. 2006) and Atlantosuchus coupatezi (Jouve et al. 2008a), A. guajiraensis possesses striations on at least some of its teeth, unlike the smooth surfaces of the teeth of C. improcerus (Hastings et al. 2010) or described for Chenanisuchus lateroculi (Jouve et al. 2005a). Teeth of A. guajiraensis are only weakly laterally compressed at certain portions of the jaw ( F ig. 3 7), not strongly laterally compressed as described for C. lateroculi (Jouve et al. 2005a).
86 Dorsal Vertebra. In ventral view, the centrum of UF IGM 37 exhibits the hourglass shape typical of Dyrosauridae (Schwarz et al. 2006). For A. guajiraensis the ventral width at the central constriction is 64 per cent shorter than at the caudal margin, very similar to that described for Hyposaurinae (2 3 or 67 per cent). In lateral view, UF IGM 37 has a centrum with a height length ratio of 71 per cent, which makes it more similar to the 2 3 ratio of the post eighth dorsal vertebrae of Hyposaurinae, as opposed to 1 3 for the first through eighth (Schwarz et al. 2006). Also in lateral view, the length of the centrum when measured along the ventral margin is 3 per cent shorter than when measured at the neurocentral suture, similar to the 5 per cent stated for Hyposaurinae (Schwarz et al. 2006). The placement of the small rounded tubercle on the anterior surface of UF IGM 37 at the lower right centre of the anterior articular facet is unique among described dyrosaurid taxa ( Fig. 3 8). Tubercles have only been mentioned once before for dorsal vertebrae: a dorsal vertebra of Congosaurus was described as having a circular dorsomedially positioned tubercle (Schwarz et al. 2006). However, tubercles have been mentioned for other segments of the vertebral column. Schwarz et al. (2006) mention a very dorsally placed tubercle on the anterior articular surface of a cervical vert ebra of Dyrosaurus sp., SMNK PAL 3826 55 94. Tubercles have also been described on the sacral vertebrae of Dyrosaurus sp., SMNK PAL 3826 69 94, and Hyposaurus YPM 753 (Schwarz et al. 2006). Sacrum. Schwarz et al. (2006) mention two parallel, dorsoventrally oriented sulci present on the caudal surface of the second sacral vertebrae that appear not to be p resent in UF IGM 35. As in Dyrosaurus sp. (SMNK Pal 3826 69 94), the second
87 sacral rib of UF IGM 35 is hourglass shaped in ventral view ( F ig. 3 9). As in D. maghribensis the second sacr al rib of UF IGM 35 covers nearly the entire lateral surface of the second sacral vertebra (Jouve et al. 2006). Ilium. The ilium of UF IGM 38 possesses a dorsal iliac wing similar to Congosaurus (Schwarz et al. 2006) and cf. Hyposaurus (Storrs 1986), i n that the indentation caudal to the craniodorsal tubercle is very slight, with the rest of the margin being smooth and shallowly convex. In Hyposaurus natator (Troxell 1925), there is a broad concavity caudal to the craniodorsal tubercle. However, the concavity cranial to the craniodorsal tubercle is much stronger in UF IGM 38 than it is in either C ongosaurus or cf. Hyposaurus and is more similar to the concavity seen in Hyposaurus natator Ischium. The ischium of UF IGM 38 is also more similar to that of Hyposaurus natator (Troxell 1925, fig. 11; YPM 753) than that of other known dyrosaurids. Neither UF IGM 38 nor YPM 753 is completely preserved, but the preservation of UF IGM 38 suggests the same thin recurved, narrow shaft interpreted for H. natator ( Fig. 3 10), not the robust thick, vertically oriented column seen in Dyrosaurus sp. (SMNK 382673 94; Schwarz et al. 2006) or D. maghribensis (OCP DEK GE 252 and 254; Jouve et al. 2006). The ischium of Acherontisuchus has a more slender shaft than D. maghribensis as measured by the ratio of the minimum anteroposterior width of the ischial shaft to the proximodistal shaft length from the level of the craniolateral depression, below the articulation for the pubis, to its distal most extent ( A. guajiraensis 0.31 for UF IGM 38; D. maghribensis 0.45 for OCP DEK GE 2 54 and 0.57 for OCP DEK GE 254, as determined from fig. 17 in the study by Jouve et al. 2006). In addition, the ischial shaft of
88 A. guajiraensis is more slender relative to the ilium than in D. maghribensis as measured by the ratio of minimum anteroposter ior width of the ischial shaft to anteroposterior length of the ilium ( A. guajiraensis 0.25 for UF IGM 38; D. maghribensis 0.36 for OCP DEKGE 254 and 0.35 for OCP DEK GE 252, as determined from fig. 17 in the study by Jouve et al. 2006). Preservation of Dyrosaurus sp. (SMNK 3826 73 94) is too incomplete for these ratios to be measured. Were the unpreserved portion to flare out (unexpectedly), the shape would still be much narrower than that seen in Dyrosaurus The angle between the articulation points of the ischium and pubis for A. guajiraensis is around 90 degrees, very similar to that figured in Troxell (1925) for H. natator (YPM 753). These are both very different from the approximately 30 degree separation reconstructed for Hyposaurinae (Schwarz Wings et al. 2009). Both Dyrosaurus and Congosaurus are known exclusively from Africa and have been d iscussed as having robust ischia (Swinton 1950; Schwarz et al. 2006). Both known ischia of the New World, H. natator and A. guajiraensis are associated with ilia that have prominent iliac craniodorsal tubercles. Ribs. A nearly complete rib associated with UF IGM 35 ( Fig 3 9) shows the clear vertical orientation, typical of Dyrosauridae, but not seen in eusuchians (Schwarz Wings et al. 2009). As in Congosaurus it bears a median crest on its lateral surface (Schwarz et al. 2006). The rib fragments are also f lat and blade like, as was described for cf. Rhabdognathus (Langston 1995). The capitular and tubercular processes are missing in all specimens, preventing further comparison. Femur. A femur, UF IGM 39, is similar to other dyrosaurid femora in its overal l sigmoidal shape and longitudinal shaft ( Fig. 3 11). Despite flattening, the fourth
89 trochanter is especially large for Dyrosauridae and the paratrochanteric fossa is deeper than the shallow pit seen in Congosaurus bequaerti (Schwarz et al. 2006). The angl e of the proximal head relative to the midline of the shaft is 52 degrees in A. guajiraensis comparable to the angle of approximately 45 degrees reported for Hyposaurinae (Schwarz et al. 2006). Metatarsal. Metatarsals are known for cf. Rhabdognathus (Lang ston 1995), Congosaurus (Jouve and Schwarz, 2004), D. maghribensis (Jouve et al. 2006) and Hyposaurus sp. (Schwarz et al. 2006), but little about their individual morphology has been published. Based on comparison to modern Alligator and cf. Rhabdognathus (Langston 1995, fig. 29), the metatarsal of UF IGM 35 seems most similar to metatarsal III, using overall shape in dorsal plantar views and the articular surface ( Fig. 3 9). P hylogenetic R elationships A matrix of 82 morphological characters (including cranial, mandibular and one postcranial charact er) was used to assess the ingroup relationships of Dyrosauridae by Hastings et al. (2010). That study included all species known from skulls and or nearly complete mandibles, for a total of 16 taxa, including 3 outgroups. The only known dyrosaurid fossi l from Europe, a mandibular symphysis fragment from Portugal, was not included in that analysis as it could not be identified beyond family (Buffetaut and Lauverjat 1978). Here I expand the matrix of Chapter 2 of this dissertation by including scores for A cherontisuchus guajiraensis for the same characters ( Appendices A and B ). The new matrix was compiled in Mesquite (Maddison and Maddison 2009) then analysed with PAUP version 4.0b10 (Swofford 2003). A new analysis was conducted with a branch and bound sear ch resulting in 15 equally most parsimonious cladograms,
90 the strict consensus of which was largely unresolved ( Fig. 3 13A). The 50 per cent majority rule consensus, however, shows a higher level of resolution ( Fig. 3 13B). The strict consensus of this anal ysis has the African Chenanisuchus as the most basal dyrosaurid ( Fig. 3 13A). No other ingroup relationships can be resolved, except for the retention of monophyly for both African Dyrosaurus and Rhabdognathus The 50 per cent Majority Rule consensus cladogram also has Chenanisuchus at the base of Dyrosauridae ( Fig. 3 13B). African Sokotosuchus and Phosphatosaurus are the next most basal members of Dyrosauridae, followed by South American Cerrejonisuchus African Arambourgisuchus is more derived than Cerre jonisuchus but more basal than the monophyletic African Dyrosaurus Dyrosaurus is sister to an unresolved clade including North American Hyposaurus rogersii South American Acherontisuchus African Congosaurus and another clade of mixed African and South American taxa. This mixed clade includes a paired African Atlantosuchus and South American Guarinisuchus with the monophyletic African genus Rhabdognathus ( R. keiniensis and R. aslerensis ). The consensus cladogram is presented in stratigraphic context as w ell ( Fig. 3 14), d isplaying all subsequent ghost lineages. The analysis by Hastings et al. (2010), using the same matrix aside from the absence of A. guajiraensis resulted in two most parsimonious trees (MTPs). Those two trees differed only in the relatio nships between H. rogersii and Congosaurus bequaerti Clearly, the poor resolution of the strict consensus presented here is the result of character conflict and a small percentage of characters coded for A. guajiraensis (15 of 82 characters were coded, 18 .3 per cent). Eleven of the 15 MPTs recovered in the analysis have A. guajiraensis as sister to or within the mixed New and Old World clade,
91 Node 8 ( F ig. 3 13; H. rogersii C. bequaerti Atlantosuchus coupatezi Guarinisuchus munizi and both species of Rh abdognathus ). Acherontisuchus shares common character states with the taxa in this clade for characters: 23 (linear maxillary margins; except for a reversal in H. rogersii ), 25 (alveolar walls level with ventral maxillary surface), 68 (fourth mandibular al veolus level with adjacent alveoli) and 71 (mandibular symphysis ends posterior to anterior 3 4 alveoli). However, A. guajiraensis falls out as sister to all of Dyrosauridae, except Chenanisuchus in 2 of the 15 MPTs, sister to a monophyletic Dyrosaurus in another tree, and sister to all of Dyrosauridae except Chenanisuchus and Dyrosaurus (Textfi g. 13B) in the last of the MPTs. Thus, a total of four cladograms have A. guajiraensis falling outside of and not sister to Node 8, reflecting the fact that its coding is more primitive for two characters: character 74 (symphysis wider than high) and character 81 (nearly constant distance between teeth from middle of maxilla mandibular symphysis). Character 1 (snout proportions) creates some separation within the taxa of Node 8 ( Fig. 3 13B), in that those of Node 9 share a reversal to the primitive state, while the other three taxa ( H. rogersii A. guajiraensis and C. bequaerti ) share the derived state. Node 9 was supported in 13 of the 15 MPTs, with the remaining two MPTs also including A. guajiraensis Nine of the 15 MPTs only differ in the relative relationships between A. guajiraensis H. rogersii and C. bequaerti D iscussion Dispersal The concept of an African origin for Dyrosauridae has existed in the literature for nearly 30 years. Buffetaut (1981) proposed an African origin and argued for a Tethyan dispersal both east and west for Dyrosauridae emanating from Africa. Hi s reasoning for this scenario stemmed from the much higher known diversity of dyrosaurids from Africa
92 than any other area, as well as ancient oceanic currents. Models of the Tethys and protoAtlantic suggested that an oceanic current flowed from Africa and Europe east to west across the protoAtlantic, towards South America, then curved towards what is now the Gulf of Mexico, continuing east along the eastern coast of North America (Berggren and Hollister 1974). Furthermore, seasurface temperatures for the Turonian (93.5 89.3 Ma) were likely very warm, around 32oC (Poulsen et al. 2001). Warm temperatures would aid in the long range dispersal of poikilothermic reptiles such as dyrosaurids. The ancient oceanic current and sea surface temperatures of the protoAtlantic waters thus explain very well the occurrences of dyrosaurids in the New World ( F ig. 3 15). In addition, a study has shown modern crocodilians ability to disperse in marine waters using their natural buoyancy to coast along currents (Campbell et al. 2010), a trait which may have been present in dyrosaurids as well. Dyrosaurid biogeography was tested empirically first by Jouve et al. (2005b). In this study, eight genera of Dyrosauridae were entered into a phylogenetic analysis, then geographic data were added to elucidate the place of origin of the family. Hyposaurus rogersii was the only representative of Dyrosauridae included from the New World. In the analysis, this North American taxon fell out as a derived relative to several African taxa, and f or this reason, Jouve et al. (2005b, 2008a) supported an African origin for dyrosaurids Jouve et al. (2008a) went on to suggest dispersal from Africa to North America, but no specific dispersal route was proposed. Hill et al. (2008) conducted a phylogenet ic analysis using an expanded version of the Jouve et al.s (2005b) matrix and also found support for an African origin of Dyrosauridae. Barbosa et al. (2008) conducted an analysis using the matrix of Jouve et al. (2005b) and proposed that
93 before the end of the Cretaceous, dyrosaurids could have crossed the Atlantic Ocean from the western coast of Africa to Brazil From there they could have dispersed northwards along the coast reaching North America and other areas of the South American continent (Ba rbosa et al. 2008, p. 1389). This dispersal hypothesis was further corroborated by Hastings et al. (2010), who also found support for multiple dispersals to the New World, based on a new cladistic analysis. Multiple dispersals are supported again by the current analysis, which shows separation of C. improcerus from the derived polytomy including all other New World taxa. Results from the current analysis, while less resolved than reported by Hastings et al. (2010), still support an African origin for Dyrosauridae. Furthermore, while far from definitive, results from the 50 per cent Majority Rule consensus cladogram have Cerrejonisuchus and A. guajiraensis separated by Arambourgisuchus and Dyrosaurus and Guarinisuchus is nested within an African clade that i ncludes Atlantosuchus and Rhabdognathus This result suggests the possibility of at least three independent dyrosaurid dispersals to the New World. Moreover, 9 of the 15 MPTs from which the 50 per cent Majority Rule tree was derived support three dispersal s, with five others supporting four dispersals. One topology suggested three dispersals with a single back dispersal from the New World to the Old World. Assuming this is correct, each dispersal would likely have taken place along similar routes from western Africa, along the paleocurrent of the proto Atlantic (Berggren and Hollister 1974) to South America ( Fig 3 15). One dispersal of a marine dyrosaurid from western Africa, during or before the Late Cretaceous (based on the Maastrichtian age of H. rogers ii F ig. 3 14) could have given rise to Acherontisuchus from the mid late Paleocene of Colombia and H. rogersii from
94 the Late Cretaceous Paleocene of North America (labelled 1 in Fig. 3 15). The H. rogersii lineage could have dispersed northward to the east coast of North America. There is a temporal problem with this hypothesis, though, in that these dyrosaurids are known from the Late Cretaceous of North America, but only the Paleocene of South America. However, this discrepancy is potentially because of s ampling bias. A second dispersal following the current of the protoAtlantic likely gave rise to Guarinisuchus from the early Paleocene of Brazil ( labeled 2 in Fig 3 15). A third dispersal would have been of a marine ancestor of Cerrejonisuchus that moved across the protoAtlantic and into Colombia sometime before the mid late Paleocene (labelled 3 in Fig 3 15). Dyrosaurids would then have dispersed from Colombia southward along a paleoshoreline, accounting for the occurrence of dyrosaurid fossils from the Paleocene of Bolivia (labelled 1 or 3 in Fig 3 15; Buffetaut 1991). Owing to the fragmentary nature of the Bolivian fossils, it is unclear which ancestral stock would have made the southward expansion, but it likely would have been the first or third because of fossils occurring in Colombia in each of these events. Owing to ocean currents moving in the opposite direction at this time (Berggren and Hollister 1974), dispersal from Europe to North America is unlikely. The dominant direction of current i n the central Atlantic is east to west, with both the north and south equatorial currents. The equatorial countercurrent flows west to east between these two currents, returning water to the eastern Atlantic (Fratantoni 2001). Owing to the older occurrence of dyrosaurids in Africa ( Fig 3 14), and the phylogenetic origin of the family in Africa, dyrosaurids likely dispersed utilizing the dominant equatorial currents, with a back dispersal along the equatorial countercurrent being unlikely.
95 Dispersal from Af rica to South America has been proposed for a diversity of vertebrate groups, which may have been assisted by the possible existence of marine islands in the central Atlantic during ocean spreading. There are a few volcanic islands in the mid Atlantic today, many of which are part of volcanic lines (e.g. Cameroon volcanic line; Aka et al. 2001) and archipelagos (e.g. Fernando de Noronha archipelago; Almeida 2002), forming linear island groupings. As Africa and South America separated, the narrow trough may have had small islands at the midocean spreading ridge, further enabling cross ocean dispersal (Carr and Coleman 1974). The east to west equatorial currents (Poulsen et al. 2001) would have assisted travel from the midAtlantic towards the South American coast. The possible existence of ancient islands in the central Atlantic has been proposed to explain dispersal in such organisms as the green sea turtle ( Chelonia mydas ; Carr and Coleman 1974). In addition, platyrrhine monkeys and caviomorph rodents made the transition from Africa to South America postcontinental separation some time prior to their first occurrences in the Oligocene (Houle 1999; Huchon and Douzery 2001; Poux et al. 2006). Ancestors of the skink genus Mabuya are thought to have immigrated t wice from Africa to South America in the last nine million years, long after the two continents separated (Carranza and Arnold 2003). Evidence for tortoise dispersal from Africa to South America post separation was found by Le et al. (2006) using mitochondrial and nuclear genes, and must have occurred before the first fossils in the Miocene (Auffenberg 1971). Perhaps most surprisingly, the burrowing amphisbaenids, or worm lizards, of the New World were found to have dispersed across the Atlantic during the Eocene, again using mitochondrial and nuclear genes (Vidal et al. 2007). Late
96 C retaceous dinoflagellates also show a strong interchange between Africa and tropical America, the Malloy suite (Lentin and Williams 1980). Finally, plants continued to have a strong interchange between Africa and South America during the Late Cretaceous, the Palmae province of Herngreen and Chlonova (1981). Paleobiology While postcrania attributed to Dyrosauridae are known from many localities, most of what has been inferred with regard to positional behaviours has come from well preserved skeletons of Dyrosaurus from the Eocene of Morocco and a nearly complete skeleton of Congosaurus from Angola (Schwarz et al. 2006). In general, dyrosaurids have been reconstructed as being s hallow, near shore marine animals utilizing axial swimming, typical of extant crocodylia, with perhaps greater tail undulatory frequency and more powerful forward thrust generated by expanded muscles of the tail (Schwarz Wings et al. 2009). The associated postcranial elements of A. guajiraensis allow for some interpretation of its functional morphology. Of particular interest is the morphology of the ribs, femur and pelvis that can reflect aspects of locomotion and respiration in crocodyliforms. As for other known dyrosaurids (e.g. Schwarz Wings et al. 2009), the ribs of A. guajiraensis are vertically orientated. This orientation has been interpreted as allowing for expanded m. iliocostalis, as well as altering the angle of attachment to the craniodorsal tub ercle of the ilium (Schwarz Wings et al. 2009). The m. iliocostalis activates during axial swimming and contributes to lateral flexion in Crocodylus porosus (Macdonald 2005), and the expanded contact for the m. iliocostalis implies its use would have been more extensive in dyrosaurids than in extant crocodylians (Schwarz Wings et al. 2009). Even if muscle force is greater in this region in dyrosaurids, range of flexion extension may have been comparable to modern crocodylians because of restrictions
97 of the osteodermal shield in this part of the trunk, as determined for other dyrosaurids (Schwarz Wings et al. 2009). The enlarged fourth trochanter of the femur, paired wi th the adjacent enlarged paratrochanteric fossa, would presumably allow for a more extensive attachment of m. caudofemoralis longus that controls hip flexion and retraction of the femur (Schwarz Wings et al. 2009). Prior to this study, ischiac blades were published for three dyrosaurids from Africa and one from North America. The ilium and ischium of UF IGM 38 are the first known from South America ( Fig 3 10), and only the second nearly complete ones from the New World. The North American dyrosaurid pelvis, YPM 753, of Hyposaurus natator (Troxell 1925; but referred to Hyposaurus rogersii by Denton et al 1997) has an elongate posteriorly angled ischium and was found in Late Cretaceous marine deposits of New Jersey ( F ig. 3 10). There is another partial pelvis of Hyposaurus natator YPM 985, but the ischial shaft was not preserved. The pelvis of dyrosaurids from the Old World consistently bears a robust, dorsoventrally orientated ischium, seen in Dyrosaurus maghribensis (OCP DEK GE 252 and 254; Jouve et al. 2006) and Dyrosaurus sp. (SMNK 3826 73 94; Schwarz et al. 2006). A nearly complete ilium and partial ischium of an indeterminate dyrosaurid (GSP 1020; Storrs 1986) was recovered from near shore marine deposits of the late Paleocene of Pakistan, but the ischial shaft is not preserved. Another pelvis was found in lagoonal estuarine sediments from the Paleocene of Saudi Arabia, but only the pubis was figured (Langston 1995), and this specimen (USGS SAP 37 CR1) does not possess the distal portion of the ischium. In extant crocodilians, the vert ebral column undergoes dorsal extension via contraction of epaxial muscles of the trunk, leading to tension in the m. ilioischiocaudalis
98 and m. rectus abdominis during locomotion. Dominant loading in this circumstance occurs during terrestrial movement whe n the weight of the body is supported only by the limbs (Schwarz Wings et al. 2009). The m. ilioischiocaudalis originates dorsally on the caudal tuber of the ilium and originates ventrally on the ventral margin of the ischiac wing ( Fig. 3 16; Schwarz Wings et al. 2009). The m. rectus abdominis does not attach to the ischium directly, but originates anteriorly at the xiphisternum and posteromost sternocostal ribs and inserts posteriorly at the pubic cartilage, which in turn serves as an attachment point for the m. ischiopubis (Schwarz Wings et al. 2009). The m. ischiopubis muscle connects the pubis with the ischium. Both m. ischiopubis and m. rectus abdominis are utilized in pitch control during diving, with higher activity when weight is added to the tail (U riona and Farmer 2008). The relatively large cross sectional area of the tall tailbase, typical of dyrosaurids (Schwarz Wings et al. 2009), and the weight associated with a larger tail may also be involved in this motion. A lteration of pitch is accomplish ed in this manner as the muscle pulls the viscera caudally, moving air in the lungs posteriorly. Air positioned more posteriorly increases the buoyancy of the posterior end of the body while simultaneously decreasing the buoyancy of the cranial end, thus altering pitch within the water column ( Fig 3 17; Uriona and Farmer 2008). Acherontisuchus guajiraensis likely had reduced surface area on the ischial shaft for muscle attachments relative to known OldWorld dyrosaurids, because of its slender shape and narrow proportions ( Fig 3 10). Despite incomplete preservation, the shape and proportions of the ischial shaft are clearly different from those of Dyrosaurus from the Eocene of Africa with a distinctly narrower shaft. The reduced size of the ischial shaft of A. guajiraensis in turn would imply reduced size and therefore less application
99 of the m. rectus abdominis and m. ischiopubis for respiration and pitch control in water. The difference in ischial shaft morphology of A. guajiraensis may in fact reflect t he freshwater habit for A. guajiraensis as inferred from the sedimentological context and associated faunas and floras, a shallow aquatic environment where these features may have been less necessary than in the deeper water marine habitat typical of dyro saurids (Denton et al. 1997). Dyrosaurus is interpreted as occupying a marine habitat as an adult (Jouve et al. 2008b) and is therefore likely a more aquatic animal than A. guajiraensis and or lived within more turbid waters, requiring greater pitchcorrection. Hyposaurus in North America may lack the robust ischial shaft because it is the primitive condition, and it is much older (Maastrichtian) than Dyrosaurus (Ypresian). A. guajiraensis likely would have occupied calmer waters and engaged in shorter di ves than Dyrosaurus requiring it to hunt either closer to the surface or in a more fluvial, terrestrial setting. This paleobiological i nterpretation is further supported by the expansion of muscle attachment in the femur and ribs for the trunk of A. guaj iraensis These features combined imply that A. guajiraensis possessed a different lifestyle from Old World hyposaurine dyrosaurids. Acherontisuchus guajiraensis likely would have been between 4.66 and 6.46 m in adult body length (Table 3 1), much larger t han the other described dyrosaurid from this locality, Cerrejonisuchus improcerus (1.22 2.22 m). Maturity in C. improcerus was confirmed using morphological features of associated vertebrae and osteoderms. Based on size, fusion of the bones in the mandible, and fusion of the sacral ribs to the sacral vertebra associated with the jaw of UF IGM 35, these size values for A. guajiraensis likely reflect adult body size. The size of A. guajirensis was therefore comparable to that
100 of Rhabdognathus keiniensis (4.72 5.44 m) and Dyrosaurus maghribensis (5.89 7.28 m), and the largest predicted values of Congosaurus bequaerti (3.97 4.66 m). A. guajiraensis was likely larger than Chenanisuchus lateroculi Guarinisuchus munizi Hyposaurus rogersii and Sokotosuchus ianwils oni Even at the largest predicted sizes, it was likely smaller than Phosphatosaurus gavialoides Arambourgisuchus khouribgaensis Dyosaurus phosphaticus and Atlantosuchus coupatezi Buffetaut (1981) described Dyrosauridae as an extinct family of particularly marine crocodyliform. However, dyrosaurids have been found previously in freshwater and potentially freshwater deposits in Burma (Buffetaut 1978b), Pakistan (Buffetaut 1978c), India (Rana 1987; Prasad and Singh 1991; Khosla et al. 2009), Sudan (Buffeta ut et al. 1990), Kenya (Sertich et al. 2006), Bolivia (Buffetaut 1991) and Colombia (Hastings et al. 2010). Dyrosaurids have yet to be found in freshwater deposits of North America. Of these records, only the Colombian dyrosaurids are known from fossils pr eserved well enough for identification beyond the family level. The sediments of the Cerrej n Formation indicate a coastal influence and may represent a transition between the marine habitat of most dyrosaurids and a more fully fluvial environment. Buffeta ut (1978c) proposed the idea that dyrosaurids may lay eggs inland then spend most of their adult life in coastal waters. Thus, the young would live inland until they reached larger size then move coastward. Buffetaut (1978c) proposed this to account for th e apparent smaller size of freshwater dyrosaurids found in Pakistan. Jouve et al. (2008b) use this same idea to account for the entirely adult fossil record of Dyrosaurus in Morocco within marine deposits. However, there does seem to be some variation, and larger dyrosaurid individuals are known from freshwater
101 deposits. In the same publication as the proposed idea, Buffetaut (1978c, p. 17 18) described the freshwater dyrosaurid vertebral fossils as such: Most of those vertebrae are rather small (about 4 c m long) for dyrosaurids, especially Eocene ones. However, a few specimens are fairly large with centra reaching a length of 7 cm and may indicate animals some 5 or 6 m long. In addition, the only known dyrosaurid fossil from Burma, found in freshwat er deposits, was described as a fairly large dyrosaurid crocodilian (Buffetaut, 1978b, p. 275). Furthermore, all specimens of Acherontisuchus and all but one of Cerrejonisuchus (Hastings et al. 2010) represent mature individuals, and not the expected bias towards immature individuals had the area been a nesting ground. Within this environment, Cerrejonisuchus was a more generalized, small bodied dyrosaurid likely preying upon lizards, snakes and small mammals (Hastings et al. 2010). On the other hand, Ach erontisuchus was a larger, more specialized piscivorous dyrosaurid. So far, dipnoan and elopomorph fossil fishes have been recovered from Cerrej n and were likely prey sources for Acherontisuchus At least in this region of the world, but possibly other regions as well, mature individuals appear to live and specialize within freshwater environments; especially considering the large size of Acherontisuchus relative to other dyrosaurids (Table 3 1), it seems likely that at least some large dyrosaurids regular ly inhabited inland waters.
102 T able 31. Snout proportions of all members of Dyrosauridae with material complete enough for skull length estimation. Owing to the incomplete nature of Acherontisuchus guajiraensis, skull lengths of the two mostly complete sp ecimens (UF IGM 34 and 35) were estimated from the preserved mandibles, resulting in possible ranges of size and proportion, based on longest and shortest reasonable dorsal skull lengths. The preorbital skull lengths of these two specimens represent the shortest possible snout for the minimum dorsal skull length and longest possible for the maximum length, resulting in a minimum and maximum ratio of preorbital skull length to dorsal skull length. DL, dorsal skull length; PreoL, preorbital skull length; R, ratio of preorbital skull length to dorsal skull length; TBL, estimated total body length using method described by Sereno et al. (2001). Citations are marked by numbered superscripts: 1Hastings et al. (2010); 2Jouve et al. (2005a); 3an estimation from th e study by Jouve et al. (2008b); 4an estimation from figure 2 in the study by Barbosa et al. (2008); 5Jouve et al. (2005b); 6Jouve et al. (2006); 7Jouve et al. (2008a). DL (cm) PreoL (cm) TBL (m) Cerrejonisuchus improcerus 31) 1 31.4 17.2 54.78 1.72 2.22 Cerrejonisuchus improcerus 1 25.8 15.3 59.30 1.22 1.79 Chenanisuchus lateroculi 2 57.6 36.5 63.37 3.57 4.24 Acherontisuchus guajiraensis 77.5 86.3 55.74 60.37 5.04 6.46 Acherontisuch us guajiraensis 72.4 78.7 57.87 64.52 4.66 5.87 Congosaurus bequaerti 3 63 41 65.08 3.97 4.66 Guarinisuchus munizi 4 47.1 30.8 65.41 2.79 3.43 Hyposaurus rogersii 2 42.9 28.2 65.73 2.48 3.11 Sokotosuchus ianwilsoni 2 60.1 39.7 66. 06 3.75 4.44 Phosphatosaurus gavialoides 2 107 72 67.29 7.22 8.05 Arambourgisuchus khouribgaensis 5 100 71.5 71.50 6.71 7.51 Dyrosaurus phosphaticus 2 104 75 72.12 7.00 7.82 Dyrosaurus maghribensis 6 89 97 73.00 5.89 7.28 Rhabdognathus keiniensis 2 73.1 53.4 73.05 4.72 5.44 Atlantosuchus coupatezi 7 104.5 83 79.43 7.04 7.86
103 F igure 3 1. Geographic and stratigraphic position for the localities of all known fossils of Acherontisuchus guajiraensis A ) map of Colombia, star marks location of the Cerrej n coal mine, the locality from which all A. guajiraensis fossils were recovered. B ) stratigraphic column of the Cerrej n Formation; fossils of A. guajiraensis were recovered from underclays immediately below the coal seams marked by arrows. All fossils dis covered thus far of Cerrejonisuchus improcerus have been from the underclay of Coal Seam 90. Stratigraphic column from Jaramillo et al. ( 2007 )
104 Fig ure 3 2. UF IGM 34, holotype of Acherontisuchus guajiraensis A B ) UF IGM 34 maxillary fragments in dorsal view. C D ) UF IGM 34 maxillary fragments in ventral view. Scale bar represents 10 cm.
105 Fig ure 3 3. UF IGM 34, holotype of Acherontisuchus guajiraensis from the Cerrej n coal mine of northeastern Colombia, middle late Paleocene. A B ) UF IGM 34 mandible in dorsal view; C D ) UF IGM 34 mandible in ventral view. Abbreviations: fa, foramen aerum; d, dentary; d7 d8, seventh and eighth dentary alveoli; sa, surangular; sp, splenial. Dotted lines are used to indicate sutures that were unclear. Scale bar represents 10 cm.
106 Figure 3 4. Referred mandible in dorsal view of Acherontisuchus guajiraensis UF IGM 35, from the Cerrej n coal mine of northeastern Co lombia, middle late Paleocene. Abbreviations: ang, angular; art, articular; d, dentary; d7, 8, 12, 14, 16, 22, provided in Terms and Anatomical Abbreviations section; md, maxillary depressions; pmf, partial mandibular fenestra; sa, surangular; sp, splenial Dotted lines indicate sutures which were unclear. Scale bar represents 10 cm.
107 Figure 3 5. Partial mandibular symphysis (UF IGM 36) referred to Acherontisuchus guajiraensis from the West Extension pit of the Cerrej n coal mine in northeastern Colombia, middle late Paleocene. A ) dorsal view; B ) ventral view. Scale bar represents 10 cm.
108 Figure 3 6. Referred mandible of Ache rontisuchus guajiraensis UF IGM 35, left articular region only. A ) in dorsal view; B ) in medial view; C ) in lateral view. Abbreviations: ang, angular; art, articular; gf, glenoid fossa; lsrap, lateral shelf of the retroarticular process; sa, surangular. Scale bar represents 10 cm.
109 Figure 3 7. UF IGM 34, holotype of Acherontisuchus guajiraensis A ) associated tooth in lingual view; B ) same associated tooth from A in posterior view, with its carina labelled; C ) associated tooth in lingual view; D ) asso ciated tooth in labial view with striations labelled; E ) associated rib fragment; F ) associated rib fragment. Scale bar represents 5 cm.
110 Figure 3 8. Referred dorsal vertebra, UF IGM 37, of Acherontisuchus guajiraensis from the West Extension pit of the Cerrej n coal mine in northeastern Colombia. This specimen was likely associated with UF IGM 36 and as such is referred to A. guajiraensis. A ) dorsal view; B ) ventral view; C ) left lateral view; D) right lateral view; E ) anterior view; F ) posterior v iew. Abbreviations: nc s, neurocentral suture; tub, tuberosity; tr pr, transverse process. Scale bar represents 10 cm.
111 Figure 3 9. Postcranial fossils associated with referred mandible, UF IGM 35, of Acherontisuchus guajiraensis A C ) second sacral ve rtebra with sacral ribs in: A ) anterior view; B ) anterior view, interpretive drawing; C ) ventral view and interpretive drawing; D F ) metatarsal (III?) in: D ) dorsal view; E ) view of proximal articular surface; F ) plantar view; G ) associated rib; H) associa ted rib. Abbreviations: 2nd sr, second sacral ribs; aafc, anterior articular facet of the centrum; dis con, distal constriction; ns, neural spine; prezyg, prezygapophyses. Dotted lines indicate sutures between sacral vertebra and sacral ribs. Scale bar rep resents 10 cm.
112 Figure 3 10. New World dyrosaurid pelvis fossils. A D ) referred left ilium and ischium, UF IGM 38, of Acherontisuchus guajiraensis from the West Extension pit of the Cerrej n coal mine in northeastern Colombia. This specimen was likely associated with UF IGM 36 and as such is referred to A. guajiraensis A ) lateral view; B ) medial view; C) lateral view of distal ischiac blade; D ) anterior view of distal ischiac blade. E G ) right ischium of Hyposaurus natator oweni (YPM 753), referred to Hyposaurus rogersii in Denton et al. (1997). E ) lateral view; F ) medial view; G ) lateral view of distal ischiac blade; H ) anterior view of distal ischiac blade. Abbreviations: ace, acetabulum; ant mar; anterior ischiac margin; art il ant, anterior artic ular surface for the ilium; art il pos, posterior articular surface for the ilium; art pub, articular surface for the pubis; f sym 1, articular surface for the first sacral rib (facies symphysialis costa sacralis 1); f sym 2, articular surface for the second sacral rib (facies symphysialis costa sacralis 2); inc acet is, incision of acetabular foramen; lin is, ischiac crest separating craniolateral and caudolateral margins of lateral surface (linea arcuata ischii); sev res, severe restriction of anterior is chiac margin; supracet cr, supracetabular crest; tubc crandors il, iliac craniodorsal tubercle. Scale bar for A B represents 10 cm, scale bar for C H equals 5 cm.
113 Figure 3 11. Referred femur, UF IGM 39, of Acherontisuchus guajiraensis from the West Extension pit of the Cerrej n coal mine in northeastern Colombia. This specimen was likely associated with UF IGM 36 and as such is referred to A. guajiraensis A ) lateral view; B ) anterior view; C ) medial view. Abbreviations: 4th tr, fourth trochanter; ic f, intercondylar fossa; pt f, paratrochanteric fossa. Scale bar represents 10 cm.
114 Figure 3 12. X Y scatter plot depicting width height ratios along the mandible, 1 being the most anterior to oth alveolus, for several genera of Dyrosauridae. The new taxon described herein ( Acherontisuchus guajiraensis ) has a wider snout in relation to the height as compared to other similar dyrosaurids. Width was measured from left to right external alveolar walls. Height was measured dorsoventrally at the midpoint of the mandible. Data for all taxa except A. guajiraensis and Hyposaurus derbianus are from Jouve (2007). Measurements for A. guajiraensis were taken from the holotype as compression of UF IGM 35 made it impractical to include. UF IGM 36 was not included as tooth position could not be reliably ascertained from the fossil.
115 Figure 3 13. Strict consensus cladograms from phylogenetic analyses of D yrosauridae. Character matrix contained 82 characters and 17 taxa, including 3 outgroup ( study by Hastings et al. 2010 and Table 2 2). A ) Strict consensus of 15 equally parsimonious cladograms from a branch and bound search using both ordered and unordered characters. Tree lengths: 172 each; C.I.: 0.541; R.I.:0.639; R.C.:0.346; H.I.: 0.459. B ) 50 per cent majority rule consensus of the same analysis; support at nodes are 1, 100 per cent; 2, 100 per cent; 3, 73 per cent; 4, 73 per cent; 5, 73 per cent; 6, 73 per cent; 7, 100 per cent; 8, 73 per cent ; 9, 87 per cent; 10, 87 per cent; 11, 100 per cent.
116 Figure 314. Majorty rule consensus tree of phylogenetic analysis placed in stratigraphic and palaeobiogeographic context. Geologic dates from Gradstein et al. (2004).
117 Figure 315. Proposed routes f or three independent dyrosaurid dispersal events from Africa to the New World. Numbers correspond to dispersal descriptions provided in text. Symbols: squares, Late Cretaceous dyrosaurids; circles, Paleocene dyrosaurids; diamonds, areas that have both Late Cretaceous and Paleocene dyrosaurids. Map of Late Cretaceous from Scotese (2001).
118 Figure 3 16. Reconstruction of skeleton of Acherontisuchus guajiraensis with muscle attachments to pelvic region. Fossil is UF IGM 38, skeleton and muscle attachments modified by Schwarz Wings et al. (2009). Pubic bone is not preserved, and its girth and length are estimated here based on pubic bones figured by Schwarz Wings et al. (2009). The angle of attachment of the pubis is based on the preserved articulation point of UF IGM 38.
119 Figure 3 17. Pitch regulation in a generalized dyrosaurid crocodyliform. A ) lungs are compressed towards the anterior portion of the pleural cavity, resulting in reduced buoyancy of the posterior end of the body and thus a less linear position B ) pleural cavity is pulled posteriorly, resulting in greater buoyancy for the posterior portion of the body and a more linear position.
120 CHAPTER 4 A NEW BLUNT SNOUTED DYROSAURID ( CROCODYLOMORPHA, MESOEUCROCODYLIA) FROM THE PALEOCENE OF COLOMBIA I ntroduction Crocodylomorpha has long been considered a living fossil group ( McGregor, 2005). This largely stems from the fact that they have displayed conservative morphology in maintaining at least some members within the same body plan as extant crocodylians since shortly after the group arose ( Ross, 1989) However, numerous instances of incredibly varied morphology have evolved time and again within the crocodylomorph lineage. Forms have varied from slend e r terrestrial ancestors (e.g. Sphenosuchus ; Walker, 1 990 ), to heavily armored forms ( Armadillosuchus ; Marinho and Carvalho, 2009) to fully marine with paddled feet and short powerful jaws skulls ( Dakosaurus ; Gasparini et al., 2006) Dyrosauridae however was thought to have occupied only a single ecological n iche that of a large near shore marine longirostrine piscivore with the only variation being younger individuals residing in limited freshwater deposits (Jouve et al., 2008b) Hastings et al. (2010) published findings that Dyrosauridae had a dwarf species residing in freshwater habitats in adulthood. Hastings et al. (2011) discussed the discovery that Dyrosauridae was successful as large bodied pisciovores in freshwater as well, while maintaining the longirostrine skull shape. Both of these findings pertai ned to the freshwater deposits of the middle Paleoceneaged (58 60 million years ago) Cerrejn Formation in northeastern Colombia ( Jaramillo et al., 2007; Fig. 4 1) These f ossils are preserved with an early tropical rainforest (Wing et al., 2009) from sed iments deposited in a large river system that drained into what is now the Caribbean Sea.
121 Dyrosauridae managed to persist through the Cretaceous extinction event and ultimately bec a me more diverse afterward (Jouve et al., 2008b). T he ability of dyrosaurids to inhabit both marine and fresh water may have contributed to their preferential survival (Jouve et al., 2008b) Isotopic values for carbon and oxygen may provide empiracle evidence for a freshwater habitat supporting this hypothesis ( Wheatley, 2010). D escribed here is a new genus and species of Dyrosauridae with a very different skull shape to other dyrosaurids The first skull of this new dyrosaurid (referred specimen UF/IGM 69) was discovered in 2005, but the skull was missing its anterior end Preser vation of the posterior incisive foramen indicated the individual likely had a short snout. A second skull with the anterior snout preserved was discovered in early 2007 and indeed this skull exhibited a very short snout while maintaining diagnostic charac ters of Dyrosauridae. Two more skulls were discovered later in 2007 bringing the minimum individuals discovered thus far to four. All specimens of the new taxon are currently curated at the University of Florida, Florida Museum of Natural History (UF), and the Instituto Nacional de Investigaciones en Geociencias, Minera y Quimica (IGM) Each specimen has been assigned a unique number with a cross listing for both collections using the abbreviation UF/IGM. Institutional Abbreviations IGM, Instituto Nacional de Investigaciones en Geociencias, Minera y Quimica, Bogot, Colombia; NJSM, New Jersey State Museum, Trenton, NJ, USA; UF, University of Florida, Florida Museum of Natural History, Vertebrate Paleontology collection, Gainesville, FL, USA ; USGS SAP, U.S. Geological Survey Saudi Arabian collection.
122 Terminology and Anatomical Abbreviations Teeth and alveoli will be referred to by number with 1 being the most anterior. Premaxillary teeth and alveoli will have the initial pm, maxillary teeth and alveoli wil l use m, and dentary teeth and alveoli will use d. For example, the first tooth or alveolus of the premaxilla will be referred to as pm1 and the second tooth or alveolus of the maxilla will be referred to as m2 Systematic Palaeontology Crocodylomorpha Walker, 1970 Crocodyliformes Hay, 1930 Mesoeucrocodylia, Whetstone and Wybrow, 1983 Dyrosauridae, de Stefano, 1903 Unnamed Taxon, N ew G enus and S pecies Diagnosis. Possesses the following apomorphies : (1) a snout that is 44 53% of overall skull leng th; (2) rugose orbital tuberosities anterior to medial margin of orbits ; (3) osteoderms that are dorsoventrally thick, unpitted, and not imbricated; (4) premaxillae that are wider than long; and (5) external nares that are wider than long. F urther differ s from all other dyrosaurids in the following unique combination of characters: (1) posterior parietal margin straight; (2) interfenestral bar wide; (3) 8 10 maxillary teeth, 5 7 of which are antorbital; (4) strong constriction at the premaxillamaxilla su ture; (5) nasal prefrontal and nasal lacrimal sutures subequal in length; (6) orbits laterally placed; and (7) teeth that are robust, round, and weakly striated.
123 Holotype. UF/IGM 67, n early complete skull from premaxilla to occipital condyle ( missing medial portion of pterygoids and ventral braincase) 9 ribs, 7 vertebrae, and unidentifiable bone Paratype. UF/IGM 68, skull from partial premaxilla to occipital condyle ( missing pterygoids and ventral braincase) right articular, 5 osteoderms, 5 vertebrae, 8 ribs, distal pubis, distal ischium, haemal arch, 3 isolated teeth, proximal phalanx, sacral rib, and unidentifiable bone. Referred s pecimens. UF/IGM 69, skull from peri orbi tal snout to posterior parietal ( missing all but a fragment of the pterygoids and t he ventral braincase) UF/IGM 70, skull from premaxilla to quadratic condyles ( missing pterygoids and ventral braincase) Type l ocality and h orizon. The holotype and all known specimens of Unnamed Taxon were recovered from a single stratigraphic layer, broadly exposed within the Cerrejn coal mine, Guajira Department, northeastern Colombia. The fossils were discovered in the underlying clay layer below Coal Seam 90 (Fig. 4 1). The geologic setting is of finegrained, gray clay and mud with fragmented lignit e interspersed throughout (Jaramillo et al., 2007) The geologic setting is indicative of a large fluvial floodplain, likely supporting abundant large plant life. The age of the layer is middle Paleocene, betwe en 58 and 60 million years old (Jaramillo et a l., 2007) Descripti on General The rostrum is very stout and short in all specimens of Unnamed Taxon, representing between 44% and 53% of the total skull length (Table 41) The overall shape of the skull is more square than triangular and is most apparent in the holotype (Fig. 42) and the paratype (Fig. 43) Each of the skulls possesses wide and
124 rugose tuberosities immediately anterior to the orbits These orbital tuberosities are most pronounced in UF/IGM 69 (Fig. 4 4) and appear to be variable as to whether they are fully on the prefrontal, lacrimal, or split between the two. The orbital tuberosities are dorsoventrally shor t and roughly conform to the contour of the skull (Fig. 4 5 ) The skull table is flat and broad, comprising most of the posterior half of the skull. The posterior margin is transversally straight. Cranial o penings. The external nares are wider than long and completely surrounded by the premaxillae with lateral margins that are ventral to both the anterior and posterior margins. No portion of the incisive foramen is preserved on any specimen. The orbits are widely spaced from the midline, in a more lateral position (Figs. 4 2 to 44) The supratemporal fenestrae are very large, much larger than the orbits, and anteroposteriorly elongat e The infratemporal fenestrae are also laterally placed, with minimal dorsal exposure and are bound anteroventrally by the jugal and posterodorsally by the quadratojugal. The suborbital fenestrae are bordered by the palatine and maxilla and are anteriorly concave. Premaxilla. The premaxilla is wider than long and completely surrounds the external nares, excluding the nasal from contact with the external nares The premaxilla possesses four alveoli, although they are not well preserved in any specimen. The third premaxillary tooth is by far the largest and the fourth premaxillary appears to be severely reduced. There is a strong indentation of the lateral margin at the premaxillamaxilla suture. Maxilla. The maxilla makes broad contact with the premaxilla, nasal, and lacrimal in Unnamed Taxon along its dorsal snout. The maxilla broadly contacts the
125 palatine on the palatal surface. Eight maxillary alveoli are preserved in UF/IGM 67 and 68 (Figs. 4 2 and 43) A portion of the posterior maxilla may be missing i n all of the specimens, so a complete count is not possible. The first, third, and fourth maxillary alveoli appear to be the largest The fifth seventh alveoli are smaller, but the 8th appears to be more robust. Even the posteromost alveoli appear uncompressed, and retain the rounded shape of the anterior alveoli. The maxillary margin is modestly sinuous (nonlinear) in dorsal appearance. Nasal. The nasal is variably fused in Unnamed Taxon. The nasals are unfused in UF/IGM 67 and 68 (Figs. 4 2 and 43) but fully fused in UF/IGM 69 (Fig. 4 4) The bone is broad and medially placed expanding from a narrow tip within the premaxilla and extending posteriorly into a rather straight margin with the frontal. The nasal does not reach the external nares. Lacrimal. T he lacrimal forms much of the anterior margin of the orbit, and is anteroposteriorly thin. The lacrimal prefrontal contact appears to be greater than the lacrimalnasal contact. The length of contact is similar between the prefrontal nasal and the lacrimal nasal sutures. Prefrontal. The prefrontal contributes largely to the medial margin of the orbit as well as to the overall interorbital width in Unnamed Taxon. The frontal prefrontal contact is extensive and penetrates broadly into the frontal, rather than being slender and reduced. Jugal. The jugal makes up the lateral margin of the orbit. The postorbital bar is missing or obscured in each of the specimens. The jugal extends posteriorly to its contact with the quadratojugal in the posterolateral corner of the infratemporal fenestra.
126 Frontal. The frontal is roughly cruciform, with an anterior projection penetrated by the paired nasals. The frontal largely contributes to the medial margin of the orbit and has a broad contact with the prefrontal. The frontal i s slightly ornamented and forms a broad bar on the lateral side where it joins with the postorbital on the posterior margin of the orbit. The frontal contributes to about one quarter of the overall length of the interfenestral bar in UF/IGM 67 (Fig. 4 2) a nd closer to one half in UF/IGM 69 (Fig. 4 4) Palatine. The palatine extends anteriorly on the palate to the level of the fifth to fourth maxillary tooth. The palatine forms the wide bar extending posteriorly from the palate toward the braincase and also forms the medial margin of the suborbital fenestra. The maxilla palatine suture occurs at the anteromedial corner of the suborbital fenestra, with the palatine contributing very mi nimally to the anterior margin. Parietal. The parietal forms the largest contribution to the skull table which is ornamented with a shallow divot on the triangular posterior section between the supratemporal fenestrae. The parietal contributes between half and threequarters to the length of the interfenestral bar. The interfenes tral bar is square in cross section, with a slight overhang. The posterior margin of the parietal is transversally straight. Postorbital. The postorbital forms the anterolateral portion of the supratemporal fenestrae and does not appear to contact the pari etal on the dorsal surface. The anterolateral process is well developed in UF/IGM 68, and modest in both UF/IGM 67 and 69. Squamosal. The squamosal forms the posterolateral portion of the supratemporal fenestrae. The squamosal and postorbital appear to contribute roughly equally to the lateral bridges of the skull table The posterodorsal prong of the
127 squamosal is most pronounced in UF/IGM 68 and extends posteriorly to the level of the posterior end of the occipital tuberosities (Fig. 4 3) However, the oth er two specimens have much more reduced squamosal projections. Pterygoid. The pterygoid is flattened onto the braincase of UF/IGM 67, but clearly shows a well developed wing extending laterally from the midline (Fig. 4 2) A fragment of this wing is also preserved in UF/IGM 68 (Fig. 4 3) The suture with the ectopterygoid forms a distinct, posteriorly directed angle. Ectopterygoid. The ectopterygoid is firmly sutured to the pterygoid and connects this bone to the maxilla and jugal. The bone forms the poster olateral portion of the suborbital fenestra. Exoccipital. The exoccipital has wide lateral expansion and constitutes much of the posterior surface of the braincase. The exoccipital has a large contribution to the occipital condyle, best preserved in UF/IGM 68 (Fig. 4 3) Well developed, wide and flat occipital tuberosities extend from the occipital surface, just ventral to the skull table. Basioccipital. The basioccipital f orms most of the wide occipital condyle It has an oblong, smooth and rounded surfac e with a strong ventral lip where the surface recurves dorsally. No portion of the basioccipital tubera is preserved. Basisphenoid. A small portion of the basisphenoid is preserved in UF/IGM 67, but lacks any part of the eustachian foramen (Fig. 4 2) It is situated between the pterygoid and the exoccipitals, and makes at least some contact with the basioccipital. Quadratojugal. The quadratojugal reaches to the posteriormost portion of the skull and contributes at least onequarter to the craniomandibular joint. This bone forms
128 the posteromedial margin of the infratemporal fenestra and extends anteriorly to the postorbital, ventral to the skull table. Quadrate. The quadrate forms around threequarters of the craniomandibular condyle as well as much of the braincase. The quadrate extends dorsally to at least the squamosal, but possibly the postorbital. Dentition. The in situ teeth of UF/IGM 67 are wide, blunt, and at least one tooth has a well preserved carina that defines the labial and lingual surfaces (Fig 4 2) The teeth preserved with UF/IGM 68 also show striations present and the well developed carina (Fig. 4 3) These teeth are all blunt and low crowned, without any preserved elongate or recurved teeth either in situ or associated with any of the speci mens. The teeth vary in size, but all are roughly circular with minimal compression toward the posterior alveoli. Articular. The articular was preserved in isolation with UF/IGM 68 with no other portion of the mandible ( Fig. 4 6 ) The articular surface where it would fuse with the surangular is preserved well, but much of the retroarticular process is missing. The lateral shelf of the retroarticular process is well developed and the glenoid fossa is smooth and deeply curved. Dorsal v ertebrae. A total of 7 dorsal vertebrae were preserved with UF/IGM 67 ( Fig. 4 7 ) These appear to be more or less from a continuous series from Dorsal 4 to Dorsal 9, as well as a more posterior vertebra from around the position of Dorsal 16. Even the anteromost of these vertebrae have fully fused neurocentral sutures. The hypapophysis of the Dorsal 4 is robust, short, and lacks a parapophysis, indicating a transition to the rib cage. Dorsals 6 9 show clear attachment points for ribs on the
129 transverse processes, indicating bifurcat ed attachment surfaces The Dorsal 16 vertebra shows no articular surface for ribs, and likely represents the lumbar region of the vertebral column, posterior to the rib cage. Caudal v ertebrae. Three caudal vertebrae were found in association with UF/IGM 68 ( Fig. 4 7 ) and represent positions between Caudal 28 and 32 One of these specimens has the entire neural spine preserved which is very long and narrow The distal tip of the neural spine does not appear swollen or enlarged relative to the rest of the s haft. The centra of the caudal vertebrae are quadrangular in cross section as well as their articular facets. Cervical r ibs. Two cervical ribs were discovered with UF/IGM 68 ( Fig. 4 8 ) and represent positions around articulation with Cervical s 4 6. Althou gh compressed, the widely divergent tuberculum and capitulum inidicate a relatively vertical position of the cervical ribs in this portion of the neck The lateral surface is smooth, with an anterior surface which likely imbricated with the adjacent anteri or cervical rib. Dorsal r ibs. Most ribs preserved with UF/IGM 67 and 68 are poorly preserved and only represent partial shafts with little to no discernible morphology Two large dorsal ribs were well preserved with UF/IGM 67 though, and are figured here ( Fig. 4 8 ). These are large and robust, much like the dorsal vertebrae, with thick dorsoventral shafts. These have clearly distinct tubercula and capitula, indicating positions around Dorsal 7 and 8. These are dorsoventrally tall with thickened distal ends. Haemal arch. The single preserved haemal arch associated with the skull (UF/IGM 68) is from the mid caudal section, with a likely position between the 11th and 15th caudal vertebrae ( Fig. 4 8 ) The vertebral attachment points are split between
130 anterior (1 3.6mm long) and posterior facets (9.1mm long), indicating its position in the tail section. The bone is 73.7mm long, is constricted in lateral view ventral to the haemal canal (10.5mm wide) and flares ventrally forming a spatulate shape (max ventral width of 16.7mm) The haemal arch does not appear to articulate with any of the three preserved caudal vertebrae. Sacral r ib. The second right sacral rib is preserved with UF/IGM 68 ( Fig. 4 9 ) The iliac surface flares posterolaterally and appears to receive an anteroposteriorly oriented ridge toward the posterior end of the pelvis. Ischium. The left distal ischium is preserved with UF/IGM 68 ( Fig. 4 9 ) The anterior and posterior margins are well preserved and do not indicate flaring in either direction, but ins tead a relatively narrow termination. The bone is also very dorsoventrally straight, with little to no curvature laterally. A modest laterally deflected crest extends from the anterior distal edge which is slightly laterally offset from the anterior margin, but then curves slightly medially to form the anterior edge. Pubis. The left distal pubis was preserved with UF/IGM 68 ( Fig. 4 9 ) The entire symphyseal surface that would have joined the other pubis is preserved and reflects an angle between the pubes at around 40o. The pubis is remarkably flat, with very little arching. Phalanx. A proximal phalanx was preserved with UF/IGM 68 ( Fig. 4 10) likely pertaining to the pes, due to its elongate form. The dorsal surface is tubular with a slightly flattened lateral surface. The ventral (plantar) side has a wide longitudinal groove along the bones centerline. The articular facet is roughly ovular, with a width of
131 24.8mm and height of 15.7mm. The preserved portion is 57.1mm long, and lacks any part of the distal c ondyle. Osteoderms. The osteoderms of UF/IGM 28 are very thick and completely unpitted ( Fig. 4 11) Both dorsal and ventral surfaces are smooth, with faint grooves radiating from the center, particularly evident around the edges The osteoderms swell in toward the thickest at the middle, and are not curved upward, but are either flat ventrally or swell ventrally as well as dorsally. None of the preserved osteoderms have any indication of an imbricating surface. Comparison General The rostrum of Unnamed T axon is much shorter than that of any other known dyrosaurid (Table 4 1) Cerrejonisuchus and Chenanisuchus have much more longirostrine skulls (Jouve et al., 2005a) The skull table is large wide and flat (Fig. 4 2) as in Phosphatosaurus (Buffetaut, 1978 a) Sokotosuchus (Buffetaut, 1979) Chenanisuchus (Jouve et al., 2005a) and Cerrejonisuchus as opposed to the elongate and narrow skull table present in Hyposaurinae. The posterior margin of the skull table is transversally straight in Unnamed Taxon, but highly indented anteriorly in Rhabdognathus keiniensis (Jouve, 2007) Hyposaurus rogersii (Troxell, 1925) and Atlantosuchus coupatezi (Jouve et al., 2008a). The premaxilla and external nares of Unnamed Taxon are both wider than long, a very atypical character for Dyrosauridae. Even the relatively short snouted forms of Cerrejonisuchus and Chenanisuchus have anteroposteriorly elongate premaxillae and external nares The anterior rostrum of Unnamed Taxon is much wider than that of the other short snouted dyr osaurids, even in the case of UF/IGM 68 that has a snout only 2.5% shorter than Cerrejonisuchus
132 The rugose tuberosities near the anteromedial margins of the orbits are unusual for crocodyliforms The only other known instance of preorbital tuberosities, i s that of Caryonosuchus pricei from the Late Cretaceous of Brazil, but these are more akin to small horns ( Kellner et al., 2011). Alligatorids have highly rugose anteromedial orbital margins, roughly where the palpebral attaches, but this is not accompanie d by surrounding unpitted surfaces as in Unnamed Taxon. These may have been keratinized, but likely di d not support large structures. Cranial o penings. The external nares of all other dyrosaurids are anteroposteriorly elongate, whereas the external nares of Unnamed Taxon are transversally oval to slightly pentagonal The orbits of Unnamed Taxon are widely placed like only one other dyrosaurid, Chenanisuchus lateroculi from the Paleocene of Morocco (Jouve et al., 2005a) All other dyrosaurids have much more medially positioned orbits. The supratemporal fenestrae of Unnamed Taxon are generally wider than in hyposaurine dyrosaurids which have much more elongate fenestrae. The infratemporal fenestrae are large in hyposaurine dyrosaurids, but transversally compr essed and laterally placed in Unnamed Taxon. Premaxilla. All dyrosaurids except Unnamed Taxon possess premaxillae that are longer than wide. Unnamed Taxon instead has wide and stout premaxillae and a constriction at the premaxillamaxilla suture that is very pronounced, as in Phosphatosaurus (Buffetaut, 1978a) and very different from the gentle curvature seen in hyposaurines such as Dyrosaurus (Jouve, 2005). Maxilla. The maxilla of Unnamed Taxon comprises a similar proportion of the snout to other dyrosaur ids, even if its overall shape is very different The tooth count is
133 smaller than most dyrosaurids The tooth count of typical dyrosaurids such as Dyrosaurus maghribensis is 19 21 (Jouve et al., 2006) as opposed to eight in Unnamed Taxon and 11 in Cerrejo nisuchus Most dyrosaurids have approximately homodont teeth, but the maxilla of Unnamed Taxon, C. improcerus and Phosphatosaurus ( Buffetaut, 1978 ) have enlarged third maxillary teeth. Unnamed Taxon also has enlarged first, fourth, and eighth maxillary teeth. The maxilla of Unnamed Taxon is somewhat intermediate in terms of degree to which the lateral margin undulates In hyposaurines, the margin is linear, but in phosphatosaurines, it is much more sinuous Unnamed Taxon instead has only a slight expansion posterior to the premaxillamaxilla suture. Nasal. The nasal is fused in most dyrosaurids, including Dyrosaurus (Jouve, 2005) Congosaurus (Jouve and Schwarz, 2004) and adult specimens of Cerrejonisuchus However, Atlantosuchus coupatezi (Jouve et al., 2008a) Rhabdognathus aslerensis (Jouve, 2007) and Sokotosuchus ianwilsoni (Buffetaut, 1979) all have unfused nasals. The largest two specimens of Unnamed Taxon have unfused nasals (UF/IGM 67 and 68), while the smaller UF/IGM 69 has fully fused nasals. La crimal. The prefrontal nasal suture is longer than the lacrimal nasal suture in Dyrosaurus (Jouve et al., 2006) but the reverse is true of Congosaurus (Jouve and Schwarz, 2004). Unnamed Taxon appears to have an intermediate condition with roughly equal pr oportions of contact to the nasal. Prefrontal. The prefrontal frontal contact of Unnamed Taxon is much longer and extensive than the reduced state of most dyrosaurids such as Congosaurus (Jouve and
134 Schwarz, 2004) and Dyrosaurus (Jouve, 2005) and most simi lar to Chenanisuchus lateroculi (Jouve et al., 2005a). Unnamed Taxon is also most similar to C. lateroculi in prefrontal contribution to interorbital width. Jugal. The jugal is thicker and more robust than that of all hyposaurine dyrosaurids (Troxell, 1925; Jouve and Schwarz, 2004; Jouve et al., 2005b, 2006, 2008; Jouve, 2005, 2007; Barbosa, 2008). Frontal. The frontal in most dyrosaurids comes to a point anteriorly, bifurcating the nasals, which can be found in Dyrosaurus maghribensis (Jouve et al., 2006) and Congosaurus bequaerti (Jouve and Schwarz, 2004). However, Unnamed Taxon has nasals which instead slightly bifurcate the frontal Alternatively, in Cerrejonisuchus improcerus the nasal terminates along a relatively straight suture with the frontal, as in UF/IGM 69 (Fig. 4 4) Palatine. The palatine of Dyrosaurus (Jouve et al., 2006) and Rhabdognathus (Jouve, 2007) meets the maxilla slightly more laterally than in Unnamed Taxon, coming to the anterior point of the suborbital fenestra Overall the palatin e reaches anteriorly to similar levels, around the halfway mark of the maxillary tooth row. Parietal. The interfenestral bar of dyrosaurids is typically T shaped and thin, as in Dyrosaurus phosphaticus (Jouve, 2005) and Arambourgisuchus khouribgaensis (Jou ve et al, 2005b) or forms a thin sagittal crest as in Rhabdognathus aslerensis (Jouve, 2007) In Unnamed Taxon, C. improcerus and C. lateroculi the interfe nestral bar is much more squareshaped and robust, but still with a bit of an overhanging lip onto the supratemporal fenestra. The straight posterior margin is most similar to that of other dyrosaurids such as Dyrosaurus (Jouve et al., 2006) and Phosphatosaurus
135 (Buffetaut, 1978a) and differs from the anteriorly indented margins of Rhabdognathus keiniensis (Jouve, 2007) and Hyposaurus rogersii (Troxell, 1925) Postorbital. Dyrosaurids typically have well developed anterolateral postorbital processes, as in Dyrosaurus phosphaticus (Jouve, 2005) but are reduced in Phosphatosaurus gavialoides (Buffetaut, 19 78a) and practically non existent in Chenanisuchus lateroculi (Jouve et al., 2005a) Squamosal. The degree of posterior projection of the squamosals is most similar to those of Dyrosaurus (Jouve et al., 2006) and not nearly as pronounced and elongate as R habdognathus aslerensis (Brochu et al., 2002). Pterygoid. The pterygoidian wing of UF/IGM 67 is broad and flat (Fig. 43), and its relative thickness may be similar to that of Dyrosaurus maghribensis (Jouve et al., 2006), but preservation makes it difficul t to discern. Ectopterygoid. The ectopterygoid of UF/IGM 69 (Fig. 4 4) does not appear twisted as in D maghribensis (Jouve et al., 2006) but is instead thick and linear. Exoccipital. The exoccipitals of all dyrosaurids contribute largely to the occipital condyle ( Jouve et al., 2006), and that of Unnamed Taxon is no exception. The occipital tuberosities are developed to varying degrees within Dyrosauridae. Unnamed Taxon is similar to Chenanisuchus and Sokotosuchus in having wide and flat tuberosities, but d iffers from Rhabdognathus and Hyposaurus that have elongate and narrow tuberosities (Jouve et al., 2005a). Basioccipital. The basioccipital differs from that of Cerrejonisuchus in being less arched dorsally and lacking the wide flat anteroventrally directed tuberosity on the ventral surface.
136 Basisphenoid. The basisphenoid is not well preserved, but does appear constricted laterally in ventral view as that of Dyrosaurus maghribensis (Jouve et al., 2006). Quadratojugal. The quadratojugal participates to the c raniomandibular joint in a similar capacity around one quarter as D maghribensis (Jouve et al., 2006). Quadrate. Quadratic crests are understated in Unnamed Taxon, if present at all, much like that of Cerrejonisuchus improcerus differing from the promi nent crest in A rambourgisuchus khouribgaensis (Jouve et al., 2005b), Rhabdognathus aslerensis (Brochu et al., 2002), and Rhabdognathus keiniensis (Jouve, 2007) Dentition. The dentition of Unnamed Taxon is most similar to that described for Phosphatosaurus (Buffetaut, 1978a) in being round and blunt and differ from the elongate recurved teeth typical of Hyposaurus (Denton et al., 1997) Dyrosaurus (Jouve et al., 2006) and anterior dentition of Acherontisuchus The teeth of Unnamed Taxon are also more low crowned and not spadeshaped as in the posterior dentition of Cerrejonisuchus Articular. The lateral shelf of the retroarticular process forms an Lshape in dyrosaurids (Jouve et al., 2005a), and is well represented in UF/IGM 68. The anteromedial wing desc ribed for Dyrosaurus maghribensis (Jouve et al., 2006) and Congosaurus bequaerti (Jouve and Schwarz, 2004) is also present in Unnamed Taxon althoug h much more rounded and robust. Dorsal v ertebrae. These vertebrae are all wider, larger, and more robust than any described thus far for Dyrosauridae (Schwarz et al., 2006). Vertebral series are best
137 known for Dyrosaurus but have also been described for Rhabdognathus (Langston, 1995) and Congosaurus (Jouve and Schwarz, 2004) Caudal v ertebrae. The caudal vertebr ae of Unnamed Taxon appear very similar to those described for Dyrosaurus and Congosaurus with a quadrangular shape and very long neural spines (Schwarz et al., 2006). The caudal vertebrae from this section of the tail though typically have a swelling at the distal tip in Dyrosaurus and Congosaurus while UF/IGM 68 does not. Cervical r ibs. The internal surface of the cervical ribs forms a concave trough as in hyposaurine dyrosaurids (Schwarz et al., 2006). Dorsal r ibs. The dorsal ribs of Unnamed Taxon appe ar more thick and robust than those figured for either Dyrosaurus or Congosaurus (Schwarz et al., 2006). Unnamed Taxon has dorsoventrally tall ribs, as in all other described Dyrosauridae and both Congosaurus and Unnamed Taxon have thickened distal tips. H aemal arch. The left and right articular surfaces do not appear as fully fused as in Congosaurus bequaerti (Jouve and Schwarz, 2004) and seem most similar to the unfused condition described for Rhabdognathus sp. (Langston, 1995). Sacral Rib. UF/IGM 68 exhi bits the roughly hourglass shape in ventral view typical of Dyrosauridae (Schwarz et al., 2006). As in Rhabdognathus sp. (USGS SAP 37CR1) the medial surface articulates with the sacral vertebra, but does not participate in the centrum (Langston, 1995). Ischium. The narrow distal end of UF/IGM 68 is very consistent with that of Acherontisuchus guajiraensis and Hyposaurus rogersii but not at all consistent with
138 Dyrosaurus (Jouve et al., 2006) The distal portion is much more narrow and pointed than the a nteroposteriorly long ventral margin of Dyrosaurus maghribensis Pubis. The pubis of UF/IGM 68 ( Fig. 4 9 ) is narrower (approx. 40o) than that seen in Hyposaurus rogersii of North America (approx. 5 0o; Tr oxell, 1925) However, the overall distal pubic shape is still much more similar between Unnamed Taxon and Cretaceous Hyposaurus of New Jersey than either is to PaleoceneEocene Dyrosaurus or cf. Rhabdognathus of Africa (Langston, 1995) Phalanx. The proximal articular surface appears more ovular than does t he triangular shape described for hyposaurine dyrosaurids (Schwarz et al., 2006). Osteoderms. Five osteoderms were found associated with the skull of UF/IGM 68. The se osteoderms are very different from any other published dyrosaurid osteoderms (Schwarz et al., 2006). Dyrosaurids typically have thin, slightly dorsally curved osteoderms with wide shallow pitting Pitting is consistent on dorsal, accessory, and gastral osteoderms Hyposaurus rogersii is very typical for a dyrosaurid in this respect and a representative osteoderm is shown in Figure 4 10. Many dyrosaurid osteoderms are imbricated and have a thick articular band where the one osteoderm overlaps the other. The osteoderms of Unnamed Taxon are not only atypical for Dyrosauridae, but they a re highly unusual for Crocodylomorpha, or any armored vertebrate. Osteoderms from all parts of the body are known in most crocodyliform groups, but none resemble the unpitted and thickened form seen in Unnamed Taxon. Even outside of Crocodylomorpha, osteoderms are w ell known in testudines, but are never as square, inflated, and untextured as these (pers. obs.). Osteoderms in sauropods are much more
139 conical or shaped like a thickened disc, and not rectangular (Dodson et al., 1998). Somewhat similar forms are seen in dorsal osteoderms of ankylosaurs ( Burns, 2008), but not nearly as square as in UF/IGM 68. Osteoderms in xenarthrans such as armadillos and glyptodonts have surface patterns as well, and also have very different overall shapes ( Hill, 2006 ). Phylogenetic Anal ysis Relationship to O ther D yrosaurids The morphologic data generated from Chapters 2 and 3 were combined with data for Unnamed Taxon to better understand the relationships of the Cerrejn taxa within Dyrosauridae (Appendices A and B) A cladistic analysis was conducted using branch and bound searches with the program PAUP version 4.0b10 (Swofford, 2003) The data set was small enough that branch and bound searches were pract ical, while exhaustive searches ( which are more comprehensive) were far too computa tionally intensive. The analysis used the same outgroup used for Chapters 2 and 3 ( Sarcosuchus imperator Elosuchus cherifiensis and Terminonaris robusta) to root the cladistic analysis The same characters were ordered (Appendix A) and all taxa were included in the initial analysis. With all taxa included, the initial results are presented in a strict consensus cladogram of 44 trees (Fig 4 11). This topology is not well resolved, with a large polytomy including all 15 dyrosaurid species, i.e. the ingroup Some resolution was recovered with a monophyletic Rhabdognathus and Dyrosaurus and a pairing of Sokotosuchus ianwilsoni and Phosphatosaurus gavialoides but no other relationship was retained.
140 The initial results revealed two wildcard taxa, Congosaurus and Acherontisuchus These two taxa were recovered as wildcard taxa in the analysis of Chapter 3 as well. An Adams cons ensus cladogram placed Acherontisuchus at an unresolved polytomy at the base of Dyrosauridae with Chenanisuchus and a monophyletic group including the 13 other species of Dyrosauridae. Congosaurus placed as sister to a clade uniting a monophyletic Rhabdognathus and Atlantosuchus + Guarinisuchus The reason for the unresolved status of these two taxa is that each has characters that are both derived and primitive and there are not enough coded characters to discern which is more prevalent in the taxon. Acherontisuchus coded primitively for characters : 1 ( snout less than 68% of dorsal skull length) 72 (minimal occlusal pits), and 74 (symphysi s wider than high) This taxon also possessed the derived state for characters : 23 (linear maxillary margin) 25 (alveolar walls level with maxillary surface) and 71 (mandibular symphysis ends posterior to anterior alveoli). This character conflict, com bined with only 18.3% of the characters coded for the taxon resulted in poor resolution within Dyrosauridae. Acherontisuchus is known from fragmentary cranial remains and mandibles (Chap. 3) and Congosaurus is known only from the snout section of the skull and no braincase (Jouve and Schwarz, 2004) Congosaurus too possessed primitive and derived characters. The primitive states were characters : 1 (snout less than 68% of dorsal skull length), 3 (thick anterior margin of external nares), and 14 (absence of lateral expansion of premaxilla). Congosaurus possessed more derived characters: 4 ( medially positioned orbits ), 13 ( posterodorsal premaxillary process proximal/anterior to second alveolus ), 22 ( premaxilla nearly three times longer than wide), 23 ( linear m axillary margin ), 33 ( nasal ceases posterior to first maxillary tooth), 81 ( alveoli more
141 widely space in posterior versus anterior snout ). The more derived position of Congosaurus in the Adams consensus (relative to Acherontisuchus ) is likely due to the possession of more derived character states. When the two wildcard taxa are removed from the analysis, the result is a single most parsimonious cladogram ( Fig. 4 12). This topology shows Chenanisuchus lateroculi from Africa as the most primitive dyrosaurid. The next most basal dyrosaurids are Unnamed Taxon and Cerrejonisuchus improcerus respectively The next most basal clade includes Hyposaurus rogersii as the sister tax on to S. ianwilsoni and P. gavialoides Arambourgisuchus khouribgaensis is the sister ta xon to a clade that includes a monophyletic Dyrosaurus and another nested clade which includes Atlantosuchus coupatezi + Guarinisuchus munizi and a monophyletic Rhabdognathus For Fig. 4 12, t he wildcard taxa have been given tentative positions based on t he analysis from Chapter 3 (Fig. 314) from a 50% majority rule consensus cladogram where they were placed within a polytomy with the clade including Atlantosuchus + Guarinisuchus and a monophyletic Rhabdognathus a clade also recovered in this chapters analysis. As Hyposaurus was recovered as more primitive than the analysis of Chapter 3, it is not presented as part of this polytomy in Chapter 4 Instead, the monophyletic Dyrosaurus is retained in its position as sister to the clade including Atlantosuchus + Guarinisuchus and a monophyletic Rhabdognathus The positions of Acherontisuchus and Congosaurus are denoted with a dashed line to indicate they were not part of this particular analysis, but are included to provide an approximation of where they likely f it within Dyrosauridae.
142 The pairing of Hyposaurus with Sokotosuchus and Phosphatosaurus has not been recovered in previous phylogenetic analyses In this ana l ysis, the only unambiguous synapomorphy supporting this clade is Character 45, a reversal to state 0 which is the presence of deep pits on the dorsal surface of the parietal Character 47, a pronounced anterolateral process of the postorbital unites all dyrosaurids except C henanisuchus Three characters unambiguously support the clade including all d yrosaurids except the short snouted Chenanisuchus Unnamed Taxon, and Cerrejonisuchus improcerus (Characters 7, 8, and 71). These characters are a narrow interfenestral bar, an unornamented interfenestral bar, and a mandibular symphysis which ends posterior to the anterior threequarters alveoli These three taxa are the shortest snouted individuals within Dyrosauridae (Table 4 1). Relationship of Dyrosauridae to O ther C rocodyliforms In many phylogenetic studies of crocodyliforms, longirostrine taxa group t ogether despite instances of clear convergence (Clark, 1994) C haracters largely tied to longirostry most often yield a close phylogenetic relationship (Jouve et al., 2006) A long standing problem has been the largely Jurassic aged thalattosuchians pairing with the Cretaceous pholidosaurids and Cretaceous Eocene dyrosaurids ( Jouve et al., 2006) The most primitive dyrosaurids in the analysis above were also the shortest snouted. I performed a p hylogenetic analysis to test the hypothesis that longirostrine thalattosuchians are much more primitive within Crocodyliformes than some analyses suggest, and that inclusion of the new brevirostrine dyrosaurids will result in a more disparate relationship between Dyrosauridae and Thalattosuchia. This crocodyliform analysis utilized a cladistic data set that included representatives from all major lineages
143 of Crocodyliformes (Jouve et al., 2006) and added to it the new short snouted Unnamed Taxon and Cerrejonisuchus improcerus The morphological matrix of Jouve et al. ( 2006) was chosen because 234 characters were coded a large sampling of Crocodyliformes (n=47) that included the dyrosaurids Dyrosaurus and Chenanisuchus The two Cerrejn dyrosaurids were coded and added to t he matrix (Appendix C) that was then r un with a heuristic search with 10,000 repetitions and the random seed function in PAUP version 4.0b10 (Swofford 2003) The result was 30 equally most parsimonious cladograms ( Fig. 4 13), as oppos ed to 124 in the heuristic search of Jouve et al. (2006) The overall results were similar to the results of Jouve et al. (2006) T halattosuchians shared a close relationship with dyrosaurids and pholidosaurids. All four dyrosaurids were monophyletic although the only internal resolution had Cerrejonisuchus and Unnamed Taxon as sister taxa. Following Jouve et al. (2006), the same data set was used for another heuristic search with 10,000 replicates with t he 15 characters suggested as associated with longirostry removed (characters 5, 7, 8, 12, 15, 30, 46, 47, 68, 83, 103, 150, 161, 172, and 189). The result of this analysis was very similar to the heuristic search of Jouve et al. (2006) with Thalattosuchia having a more basal position within Crocodyliformes basal to nearly all of Mesoeucrocodylia ( Fig. 4 13) Pholidosaurida e and Dyrosauridae were united in a node, but different from the previous analysis in that Elosuchus had an unresolved relationship in a polytomy including Dyrosauridae and a clade that includes all other pholidosaurids. Jouve et al. (2006) had Elosuchus a s primitive to both Pholidosauridae and Dyrosauridae. The addition of short snouted dyrosaurids did not resolve the problem of convergence driving the topology between thalattosuchians,
144 dyrosaurids, and pholidosaurids. These results suggest that these conv ergent characters are not limited to longirostry and are present even in nonlongirostrine taxa. Biogeography A biogeographic analysis was run using the dyrosaurid matrix I used the program S DIVA ( Yu et al., 2010a) which utilizes a tree file as generated by Paup ( Swofford, 2003) then the user assigns each taxon to a region. For this study, I used Africa, North America, and South America as regions A, B, and C respectively ( Fig. 4 14). The program generates a consensus cladogram from the tree file, incor porating the biogeographic region of the taxa included ( Yu et al., 2010b) The program generates likely regions of origin for the ancestors of the taxa included in the analysis. The program creates a pie chart at each of these nodes with percent probabilit y by region for the ancestor. The program can be set to allow for multiple regions to be occupied simulataneously. Four limitations of the software should be kept in mind. The first is that the program from which it was derived (DIVA ; R onquist, 1996) treat s dispersal between different regions as equally possible, with no preference for a certain direction or between certain regions ( Kodandaramaiah, 2010) The second is that the program must assign a topology with no polytomies As a result, taxa with unresolved relationships in nonbiogeographic studies should be interpreted with caution when using S DIVA (Yu et al., 2010b) For this reason both wildcard taxa recognized in the earlier analysis were not included. S DIVA utilizes phylogeny to determine dispers al, and therefore taxonomically uninformative fossils cannot be included. Thus the present analysis and discussion is limited to identifiable taxa known from nearly complete fossil skulls and does not take into account regions where nondiagnostic dyrosaur id fossils were found.
145 Finally, the program cannot incorporate temporal data, and timing of dispersal must be determined using ages of the fossil taxa. All past phylogenetic studies of Dyrosauridae have recovered an African origin for the family, and the current analysis supports this The biogeographic analysis recovered five optimized dispersal histories, with a minimum of three dispersal events from Africa to the New World within Dyrosauridae. The first of these occurred with the ancestor of Unnamed Tax on to South America ( Fig. 4 15) The second occurred with the ancestor of Guarinisuchus munizi reaching Brazil. The third independent dispersal would have been the ancestor of Hyposaurus rogersii immigrating to North America. Had Acherontisuchus guajiraens is been included, it would likely have represented a fourth dispersal, as its relationships were most often close to Arambourgisuchus and Dyrosaurus of Africa, and did not have a direct relationship with Guarinisuchus or any other New World dyrosaurid. Con gosaurus bequaerti shared a close relationship with other African taxa in the analysis of Chapter 3, and it likely only required dispersal within Africa to account for its occurrence in Angola. This interpretation excludes the occurrence of dyrosaurids known from fragmentary fossils in Asia (e.g. Buffetaut 1978b, 1978c) due to the limi tations of the analysis. Discussion Taxonomy. The new unnamed taxon can be referred to Dyrosauridae based on: (1) lateral margins of external nares lower than anterior or post erior margins; (2) supratemporal fenestrae at least twice longer than wide; (3) occipital tuberosities present, directed posteriorly, and formed by exoccipitals; (4) exoccipitals participate greatly in occipital condyle; (5) neural spines extremely elongat e dorsally in caudal vertebrae; dorsal margin of neural spines narrow, not thickened; (6) caudal centra
146 quadrangular in cross section; (7) haemal arches extremely elongate ventrally. For a list of characters discerning Unnamed Taxon from all other dyrosaur id diagnoses provided in Appendix D. Paleobiology. The orbits of Unnamed Taxon are very widely spaced for Dyrosauridae (Figs. 4 2, 4 3, and 44) Typical dyrosaurids have centrally placed orbits close to the midline of the skull (Jouve et al., 2005a) The only other dyrosaurid with widely set orbits is Chenanisuchus lateroculi (Jouve et al., 2005a). The only extant crocodylian with notably wideset orbits is Gavialis gangeticus A bivariate plot of width of skull at orbits and interorbital width (with natural log transform) reveal ed Unnamed Taxon had greater similarity in terms of orbital spacing with Gavialis than with typical dyrosaurids Alligator mississippiensis Caiman crocodilus and Crocodylus niloticus (Fig. 4 16) Extant G avialis typically acquire their prey almost exclusivel y fish, below the waters surface (Thorbjarnarson, 1990; Grenard, 1991). The three extant species with more narrowly placed orbits more commonly acquire prey from a position at the surface of the water (Grenard, 1991; Thorbjar narson, 1993). M ore widely set orbits may be tied to a nonsurficial prey acquisition feeding strategy and likely indicates a deviation by Unnamed Taxon and C. lateroculi from the t ypical behavior of dyrosaurids. The distal pubis is rare within the New Wor ld dyr osaurid fossil record and the only other figured specimen is that for Hyposaurus rogersii from the Late Cretaceous marine deposits of New Jersey (Troxell, 1925). Both have a more elongate suture between left and right pubes as compared to extant croc odylians and that of Unnamed Taxon is proportionally longer than H. rogersii The pubic cartilage attaches to the anterior portions of these bones in extant crocodylians and the symphyseal region is
147 where the ischiopubis and ischiotruncus muscles attach (Uriona and Farmer, 2008; Schwarz Wings et al., 2009). A nonenlarged distal ischium, also preserved with UF/IGM 68, indicates highly reduced attachment surfaces for the ischiopubis ischiotruncus, and ischiocaudalis muscle s (Fig. 4 8). The ischiopubis mus cle in particular is used primarily in buoyancy control (Uriona and Farmer, 2008). Much like the implications for Acherontisuchus guajiraensis (Chapter 3) it would appear Unnamed Taxon also relied less on these muscles for pitch control within the water. T he pubis is heavily utilized in extant crocodylian respiration and the bone is pulled ventrally and rotated slightly by the rectus abdominus and diaphragmaticus bringing air into the lungs ( Claessons, 2004). The pubic cartiage is what dominantly attaches these two bones in extant crocodylians (Uriona and Farmer, 2008). The longer and more rigid suture marks in Unnamed Taxon may have reduced the flexibility of this joint, but provided a firmer basis from which to depress the pubes and take in air. This firmer suture may have also meant Unnamed Taxon was less capable of pubic rotation as in extant crocodylians (Claessons, 2004). The Eocene Dyrosaurus maghribensis of Morocco possessed a pubis that is spatulate and much more similar to that of extant crocodylia (Jouve et al., 2006). The preserved ribs of Unnamed Taxon indicate similar vertical positions for muscle attachments, as indicated for Hyposaurinae (Schwarz Wings et al., 2009) and A. guajiraensis (Chapter 3). The resultant angle for axial muscles was found to imply dyrosaurids likely swam in a much more undulating fashion than extant crocodylians, which are nearly entirely tail based swimmers (Schwarz Wings et al., 2009; MacDonald, 2005). The osteoderms of hyposaurine dyrosaurids are known to imbricate dorsally,
148 providing bracing for the vertebral column. Osteoderms are not as extensive along the lateral portion of the dyrosaurid body as in some extant crocodylians, likely affording dyrosaurids greatery flexibility at the sacrifice of reduced stability and armored protection. This flexibility would have been necessary for the more undulating locomotion of dyrosaurids (Schwarz Wings et al., 2009). The osteoderms of Unnamed Taxon likely did not imbricate, implying an even greater degree of flexibility, at the sacrifice of reduced stability particularly for rostroterminal torsion. Pitting in osteoderms has been associated with thermal regulation in extant crocodyliforms, with the increased surface area and veination allowing a greater amount of heat transfer t o take place along the animals broadly exposed dorsal surface ( Seidel, 1979) B ones of the skull that are unpitted are separated from the dermis by muscle, as opposed to pitted surfaces that are very near to the dermis (Seidel, 1979) The osteoderms of Unnamed Taxon are unpitted, and likely resided deeper in the dorsal musculature th a n in extant crocodylians and were not utilized as much for thermoregulation. The small rivulets and thin crevices radiating from the center of the dorsal surface are instead likely indicative of keratinization, which has been proposed for similar features on the cranium as a display feature in the extinct crocodyliform Aegisuchus ( Holliday and Gardner, 2012) Diet. The teeth of Unnamed Taxon are blunt and robust, which may be indicative of a durophagous diet with a strong crushing bite ( Massare, 1987) A large turtle shell (UF/IGM 71) has preserved several dents, scores, and scratch marks on dorsal and ventral surfaces that resemble predation attempts by a crocodyliform ( Noto e t al., 2012 ) There are straight puncture marks, tooth slide marks, and at least one rehealed
149 puncture mark ( Fig. 4 1 7 ) The largest of these puncture marks fits very well with the largest preserved tooth (m1) of UF/IGM 67.
150 T able 4 1. Snout proportions o f all members of Dyrosauridae with material complete enough for skull length estimation. Abbreviations: DL dorsal skull length; PreoL, preorbital skull length; R ratio of preorbital skull length to dorsal skull length; TBL estimated total body length us ing method by Sereno et al. (2001). Citations are marked by numbered superscripts: 1Hastings et al. 2010; 2Jouve et al. 2005a; 3Hastings et al. 2011; 4an estimation from Jouve and Schwarz 2004; 5an estimation from figure 2 in Barbosa et al. 2008; 6Jouve et al. 2005b; 7Jouve et al. 2006; 8Jouve et al. 2008. DL (cm) PreoL (cm) R (PreoL/DL) x 100 TBL (m) Unnamed Taxon (UF/IGM 67) 62 27.5 44.35 4.58 Unnamed Taxon (UF/IGM 68) 68 35.5 52.21 5.05 Cerrejonisuchus improcerus (UF/IGM 31) 1 31.4 17.2 54.78 1.72 2.2 2 Cerrejonisuchus improcerus (UF/IGM 29) 1 25.8 15.3 59.30 1.22 1.79 Chenanisuchus lateroculi 2 57.6 36.5 63.37 3.57 4.24 Acherontisuchus guajiraensis (UF/IGM 35) 3 77.5 86.3 43.2/52.1 55.74 60.37 5.04 6.46 Acherontisuchus guajiraensis (UF/IGM 34) 3 72. 4 78.7 41.9/50.8 57.87 64.52 4.66 5.87 Congosaurus bequaerti 4 63 41 65.08 3.97 4.66 Guarinisuchus munizi 5 47.1 30.8 65.41 2.79 3.43 Hyposaurus rogersii 2 42.9 28.2 65.73 2.48 3.11 Sokotosuchus ianwilsoni 2 60.1 39.7 66.06 3.75 4.44 Phosphatosaurus g avialoides 2 107 72 67.29 7.22 8.05 Arambourgisuchus khouribgaensis 6 100 71.5 71.50 6.71 7.51 Dyrosaurus phosphaticus 2 104 75 72.12 7.00 7.82 Dyrosaurus maghribensis 7 89 97 73.00 5.89 7.28 Rhabdognathus keiniensis 2 73.1 53.4 73.05 4.72 5.44 Atla ntosuchus coupatezi 8 104.5 83 79.43 7.04 7.86
151 Figure 4 1. Locality map and stratigraphic column for locality where all known Unnamed Taxon fossils are found. A) Northern South America with star indicating Cerrejn fossil locality in northeastern Colombia. B) Stratigraphic column of Cerrejn Formation (from Jaramillo et al., 2007). Fossil locality of Unnamed Taxon is underclay below Coal Seam 90, indicated with arrow above.
152 Figure 42. Holotype (UF/IGM 67) of n ew g enus and species of Dyrosauridae from Cerrejn locality in northeastern Colombia, middle late Paleocene. A B) in dorsal view; C D) in ventral view. C) Insert displays an in situ tooth in lingual and anterior views; scale bar equals 1cm. Abrreviations: b f, bone fragment; bo, basioccipital ; bsp, basisphenoid; en, external nares; eo, exoccipital; ep, ectopterygoid; f, frontal; j, jugal; l, lacrimal; max, maxilla; m1,4,5,8, maxillary teeth/alveoli; n, nasal; or t, orbital tuberosities; ost, osteoderm (displaced); o t, occipital tuberosities; p parietal; pal, palatine; pm2 4, premaxillary teeth/alveoli; pmx, premaxilla; po, postorbital; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; sq, squamosal; s r, Serpentes indet. rib; stf, supratemporal fenestra; vert, vertebrae (displac ed). Scale bar equals 10cm.
153 Figure 43. Paratype (UF/IGM 68) of new genus and species of Dyrosauridae from Cerrejn locality in northeastern Colombia, middle late Paleocene. A B) skull in dorsal view; C) associated tooth in lingual view; D) associated tooth in posterior view; E F) skull in ventral view. Abbreviations: bo, basioccipital; en, external nares; eo, exoccipital; eo a, articulation for exoccipital; ep, ectopterygoid; f, frontal; j, jugal; l, lacrimal; max, maxilla; m1 8, maxillary teeth/alveol i; n, nasal; orb, orbit; or t, orbital tuberosities; o t, occipital tuberosities; p, parietal; pal, palatine; pm2 4, premaxillary teeth/alveoli; pmx, premaxilla; po, postorbital; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; q c, quadrati c condyle; sq, squamosal; stf, supratemporal fenestra. Scale bar for A B and E F equals 10cm. Scale bar for C D equals 1cm.
154 Figure 44. Referred skull (UF/IGM 69) of new genus and species of Dyrosauridae from Cerrejn locality in northeastern Colombia, middle late Paleocene. A B) skull in dorsal view; C D) skull in ventral view; Abbreviations: f, frontal; j, jugal; l, lacrimal; max, maxilla; m2,5 6, maxillary teeth/alveoli; n, nasal; orb, orbit; or t, orbital tuberosities; p, parietal; pal, palatine; pm2 3, premaxillary teeth/alveoli; pmx, premaxilla; po, postorbital; prf, prefrontal; sq, squamosal. Scale bar equals 10cm.
155 Figure 45. Referred skull (UF/IGM 69) of new genus and species of Dyrosauridae from Cerrejn locality in northeastern Colombia, middle late Paleocene. Oblique view of right orbital tuberosity. Abbreviations: f, frontal; j, jugal; l, lacrimal; max, maxilla; n, nasal; or t, orbital tuberosities; prf, prefrontal. Scale bar equals 10cm.
156 Figure 46 Associated articular bone of UF/I GM 68. A B ) in medial view; C D) in lateral view; E F) in dorsal view. Abbreviations: as sa, articular surangular surface of arictulation; gf, glenoid fossa; lsrap, lateral shelf of retroarticular process; rap, retroarticular process. Scale bar equals 10cm
157 Figure 47 Vertebrae associated with skulls of the new genus and species of Dyrosauridae. A B) three articulated dorsal vertebrae associated with skull of UF/IGM 67, likely positions six through eight. C D) dorsal vertebra associated with skull of UF/IGM 67, likely position 16. E F) dorsal vertebra associated with skull of UF/IGM 67, likely position four. G H) anterior view of caudal vertebra associated with skull of UF/IGM 68, likely position 28. I) same as G, but in lateral view. J) lateral view of caudal vertebra associated with skull of UF/IGM 68, likely position 30. Abbreviations: cen, centrum; hyp, hypopophysis; i t, isolated tooth; n c, neural canal; ncs, neurocentral suture; n s, neural spine; przy, prezygapophyses; pozy, postzygapophysis; t p, transverse process. Scale bar for A F equals 10 cm; scale bar for G J equals 5 cm.
158 Figure 48 Ribs and haemal arch associated with skulls of the new genus and species of Dyrosauridae. A) lateral view of dorsal ribs associated with UF/IGM 67, likely p ositions seven and eight. B) medial view of cervical rib associated with UF/IGM 68, likely between positions four and six. C) same as in B in lateral view. D) posterior view of haemal arch associated with UF/IGM 68, likely position between 11 and 15. E) same as in D in lateral view. Abbreviations: capm, capitulum; h c, haemal canal; inc ct, incisura capitulotubercularis ( capitulotubercular incision) ; p art f, posterior articular facet; tubm, tuberculum.
159 Figure 49 Portions of the pelvis of the new genus and species, UF/IGM 68. A) Distal left ischium in lateral view. B) Distal left ischium in posterior view. C) Distal right pubis in ventral view. D) distal right pubis in medial (articular) view. E) diagram showing appropriate position of ischium and pubi s in ventral view with muscle attachments overlayed, outline indicates position in body of the new genus and species. F) Second right sacral rib in ventral view. G) same as F in lateral view. Abbreviations: ant, anterior; art pub, articular surface for attachment to other pubis bone; f sym il, facies symphysialis ilii ( articular surface of the sacral rib with the ilium ) ; gas, gastralia; is, ischium; isc, ischiocaudalis muscle; isp, ischiopubis muscle; ist, ischiotruncus muscle; pub, pubis; pub car, pubic cartilage; r ab, rectus abdominis muscle. Scale bar for A D and E equals 10 cm; scale bar for F G equals 5 cm.
160 Figure 410. Proximal phalanx of the new genus and species of Dyrosauridae, UF/IGM 68. A) dorsal view; B) plantar view; C) proximal view. Scale bar for A B equals 5 cm; scale bar for C equals 1 cm.
161 Figure 41 1 Dyrosaurid osteoderms. A &C) dorsal osteoderm, UF/IGM 68, in dorsal view; B&D) same specimen as A &C in ventral view. E) another dorsal osteoderm, UF/IGM 68, in dorsal view; F) same speci men as E in ventral view; G) lateral osteoderm, UF/IGM 68, in dorsal view; H) same specimen as G in ventral view; I) dorsal osteoderm, UF/IGM 68 in dorsal view; J) same specimen as I in ventral view ; K) same specimen as I in cross section view at fracture point visible in I and J. L) osteoderm of Hyposaurus rogersii NJSM 12293, in dorsal view; M) same specimen as L in ventral view; N) same specimen as L in lateral view. Scale bar equals 5 cm.
162 Figure 41 2 Cladograms resulting from a phylogenetic analys is of Dyrosauridae. Left cladogram is strict consensus with all named species known from more than dentary fragments. Right cladogram represents single tree resulting from analysis with the two wildcard taxa removed ( Acherontisuchus guajiraensis and Congos aurus bequaerti ) Dotted lines for the wildcard taxa represent approximate placement based on cladistic analysis of Chapter 3 (Fig. 314 and Chapter 4 discussion for more information) Right cladogram is placed in stratigraphic and geographic context. Dates are obtained from Gradstein et al. (2004 ). Abbreviations: C.I., Consistency Index; R.I. Retention Index; R.C. Rescaled Consistency Index; H.I. Homplasy Index.
163 Figure 41 3 Two cladograms from analyses utilizing a matrix with representatives of all of Crocodylomorpha A) Strict consensus cladogram resulting from analysis using all 234 characters of Jouve et al., 2006. B) Strict consensus cladogram resulting from analysis that omitted the 15 characters associated with longirstry Note the very different placement of Thalattosuchia with respect to Dyrosauridae in the two analyses. Abbreviations: C.I., Consistency Index; R.I. Retention Index; R.C. Rescaled Consistency Index; H.I. Homplasy Index.
164 Figure 41 4 Cladogram resulting from biogeographic analy sis of Dyrosauridae using the program S DIVA (Yu et al., 2010a) Solid arrows indicate certain dispersal events. The dotted line indicates a possible back dispersal from South America to Africa.
165 Figure 41 5 Map showing dispersal pattern and timing for Dyrosauridae. Map is of the Late Cretaceous, colorized from Scotese (2001). There are at least three independent dispersals from Africa to the New World ( refer to text for explanation).
166 Figure 416. Bivariate plot with natural log transform of skull w idth as measured at orbit (x axis) and interorbital width of dyrosaurids and extant crocodylians.
167 Figure 41 7 P ortions of pelomedosoid turtle carapace, UF/IGM 71, with crocodyliform bite marks. A & C ) costal fragment in dorsal view; B & D ) same fragment in ventral view. E & G ) neural fragment in dorsal view. F & H ) peripheral in dorsal view. I & K ) m1 tooth from holotype of the new genus and species, UF/IGM 67, placed within the impact shell scar featured in I. J & L ) peripheral in dorsal view. Abbreviations: bm, bite mark; bm?, possible bite mark; bm&p, bite mark and regrown bone plug; dm, drag marks; m1, first maxillary tooth; p r, proximal rib; Scale bar for A H and J& L equals 5 cm; scale bar for I & K equals 1 cm.
168 CHAPTER 5 DYROSAURID MORPHOSPA CE AND DIVERSITY T HROUGH TIME Introduction The discoveries of the three new genera and species of Dyrosauridae from Cerrejn have shown a level of variation previously unknown for this family This breadth in form in one location is not unprecedented within extant Crocody lia; however the different morphotypes are usually filled by at least two distinct taxonomic groups For instance, i n Colombia and Venezuela today, there are large narrow snouted crocodiles and small shorter snouted caim ans living very near each other (Ros s, 1998). Consequently, morphospace is occupied by two distinct clades covering a span from longirostrine to brevirostrine skull morphology In terms of variation in skull shape, how varied were the dyrosaurids particularly with respect to the new freshw ater habitat, and how does this compare to extant morphospace? During the Paleocene, it would appear dyrosaurids fit the range from short to long snouted, but are they covering the same breadth as extant taxa? A metric is needed in order to understand dyr osaurids within a context of known ecology (i.e. modern). V ariance in skull shape has been quantified for Crocodylia using geometric morphometrics ( Monteiro et al., 1997; Pierce et al., 2008; Sadleir, 2009; Pearcy and Wijtten, 2011). Geometric morphometric s is a method utilized to quantify shape variation in a group by assigning a series of landmarks to anatomical positions which are present in each specimen of the group. The study by Monteiro et al. (1997) included only Caiman, but three other studies have included all living species of Crocodylia (Pierce et al., 2008; Sadleir, 2009; Pearcy and Wijtten, 2011). Each of these has found a similar spread in morphospace occupation within living crocodylians. Gharials occupy
169 the most distinctly longirostrine skul l shape and caimans the most brevirostrine. Crocodylidae occupies the widest breadth of skull morphospace within the extant species (Sadleir, 2009; Pearcy and Wijtten, 2011). This method can provide a relative metric of disparity between Dyrosauridae and C rocodylia and a test for the hypothesis of similar am ounts of morphospace occupation with the addition of the freshwater Cerrejn taxa. The question of how dyrosaurids were able to achieve their disparity within a freshwater habitat can be addressed with t hese data as well Prior to this study diagnostic dyrosaurid adults had only been found in ancient coastal/estuarine or shallow marine deposits. A hypothesis to explain only smaller (and fragmentary) individuals being found in more freshwater deposits was an allusion to the modern saltwater crocodile, Crocodylus porosus (Jouve et al., 2008b). Extant C. porosus are hatched upstream, and then become progressively more saltwater with age ( Messel and Vorlicek, 1986). Two of the dyrosaurids of Cerrejn have dis tinctly unique skull morphology for the family, while still retaining the identifying characteristics that make them dyrosaurids. The method of geometric morphometrics can address the questions of how the new freshwater dyrosaurids compare in shape to brac kish/saltwater dyrosaurids, how they compare to modern crocodylians, and whether or not ontogeny may have played a role in this diversity. By quantifying modern skulls of varying ages, one can determine what ontogenetic effects there are in skull shape wit h respect to growth. Morphologic disparity and diversity often follow similar trends through time, but one can deviate independently from the other ( Foote, 1994) Increased number of taxa
170 implies at least some amount of increased morphological differences, but these can be subtle variations and may vary differently from disparity and morphospace occupation. Dyrosaurid taxonomic diversity is greatest during the Paleocene, whether or not the Cerrejn taxa are included. Even limited to the marine/estuarine dyr osaurids, the timing of this swell in taxonomic diversity coincides with a dearth in large predatory marine tetrapods. The Cretaceous Paleogene boundary is marked by a mass extinction event ( Shulte et al., 2010), resulting in a collapse of the marine ecosy stem and ultimate extinction of most large marine reptiles ( DHondt, 2005; Motani, 2009 ). The mosasauroids and sauropterygians were dominant marine carnivores during the Late Cretaceous that went extinct at the end of the Maastrichtian (Motani, 2009). Alongside these large marine reptiles were the much smaller dyrosaurids during the Late Cretaceous ( Hill et al., 2008 ). However, while the mosasaur oid s and sauropterygians went extinct at the K Pg boundary, the dyrosaurids persisted and radiated during the Pal eocene. Dyrosauridae went extinct in the middle Eocene, coincident with the radiation of early whales ( Uhen, 2010). As whales began to diversify, they also dispersed throughout the Tethys (Uhen, 2010), into many of the locations once occupied by dyrosaurids. D iversity studies have been conducted on marine tetrapods for the Mesozoic (Benson et al., 2010) cetaceans for the Oligocene to present (Marx and Uhen, 2010), and selachiians across the K Pg transition (Kriwet and Benton, 2004). None of these studies have compared large marine carnivores across the time span of the dyrosaurids (Late Cretaceous Eocene) and dyrosaurid diversity has not been assessed.
171 In the second part of this chapter, I address the question of how diversity trends may be related between dyrosaurids and other marine carnivores through geologic time I have generated diversity values for each of these groups as well as selachiians from the Late Cretaceous through Eocene. Dyrosaurids were tested both with and without the Cerrejn taxa included, as the Cerrejn forms are not of the typical salt/brackishwater habitat of Dyrosauridae and would likely not have been occupying the same ecologic niche as mosasauroids, sauropterygians, cetaceans, and selachiians Correcting for sampling bias in mari ne fossils has been applied globally for invertebrates utilizing the Paleobiology Database (Alroy et al., 2001). These methods were later adapted for correction based on the availability of fossiliferous marine formations (FMFs) for each time period analyz ed (Smith and McGowan, 2007). The correction method was designed to adjust for the bias of certain time periods containing more/less FMFs, but focused solely on Western Europe, further incorporating rock surface area data for the region. This bias correcti on method is impractical on a global scale, as the rock area data are highly insufficient for many other regions of the world, but the overall method is still very applicable to the current study. Benson et al. (2010) adapted the analysis of Smith and McGowan (2007) for global diversity of marine vertebrates throughout the Cretaceous, focusing on number of FMFs as derived from the Paleobiology Database. Given the similarity of the current study and overlap of taxa to be included, I extended the data collect ed by Benson et al. (2010) into the Eocene and added dyrosaurids, cetaceans, and selachiians.
172 G eometric Morphometric Analysis Materials and Methods A total of 242 extant crocodylian skulls were utilized for the analysis These included individuals from mul tiple ontogenetic stages. Each living species of crocodylian is represented by at least one specimen in the dataset, but sample size per species is as high as 51. This unequal sampling by species is driven entirely by the availability of certain species wi thi n museum collections (Appendix E ). A total of 10 dyrosaurid species could be analyzed (Appendix F ) Images for d yrosaurids were based on reconstructions of each taxon under circumstances of ideal preservation. These figures are twodimensional line draw ings that have used all specimens available for the species to create an idealized skull in dorsal view with no elements missing. Sufficient line drawings were present in the literature for 8 nonCerrejn dyrosaurid species (Appendix F ). For Cerrejonisuchus improcerus and Unnamed Taxon, this meant forming reconstructions for each species. These were generated from all known specimens, trying to form a consistent morphology (Fig. 51). In both cases I used the holotype as the basic template, but filled in partially obscured or distorted areas with the morphology present in the other specimens. I utilized a form of principal components analysis, relative warps analysis, in order to quantify and compare crocodyliform skull structure. The method chosen was a two dimensional analysis. Images were first obtained for each extant crocodylian skull in dorsal view. Each skull was positioned such that the dorsal skull table was horizontal and the anterior end of the snout was raised dorsally, following the procedures of Pearcy and Wijtten (2010).
1 73 The images were compiled into a single tps file using the program tpsUtil (Rohlf, 2004). This combined tps file was then loaded into tpsDig2 (Rohlf, 2006) where 35 landmarks were placed at specific suture marker points, or landm arks. I utilized the same landmarks as Pierce et al. (2008) which were established for extant crocodylia (Fig. 5 1) The landmarks are exclusive to the midline and the left side of the skull. The reason the entire skull was not used was to reduce the effec ts of asymmetry in the analysis The dyrosaurid reconstructions are necessarily symmetrical, and thus incorporating potential asymmetry in the extant component could distort the results. The left side was chosen arbitrarily over the right. In cases where t he skull was incomplete on the left side, but complete on the right, the image was flipped through the tpsDig2 program (Rohlf, 2005), and then landmarks were assigned. This program records the position of each landmark, by number, relative to each other. S everal versions of this first tps file ( with landmarks ) were made to test for morphospace occupation in different subsets of the total sample. The reason for this is that with each group analyzed, a unique mean is formed from which all specimens will deviate Thus the mean for Dyrosauridae would be expected to be different from the mean of Crocodylia, and even different samplings of the same species would generate at least slightly different mean shapes Thus to understand the relative disparity of the subs ets, the overall group needs to be established first. A relative warps analysis was run with each tps file using the program tpsRelw (Rohlf, 2005) This analysis uses the spatial data generated by placing landmarks to compute a mean, and then produce a ser ies of relative warps data reflecting dominant variation from the mean. These data are produced in a series of relative warps from
174 greatest to least variance. Thus the sum of most variation can be presented by plotting the data for the first two relative w arps on a simple x y scatter plot Additional variation does exist beyond these two axes, but the variation is increasingly less from the mean with the higher numbered relative warps I have presented the first and second relative warps as well as the rela tive warp visualization plots generated by the same program as calculated at the end point of each of these axes These plots show the deformation of the landmarks relative to the mean in a grid format.The grid is completely undeformed at the intersection of the two axes and becomes progressively more deformed away from the axes I have presented the visualization plots for the extremes at each of the four axis tips within the plotted space, showing a hypothetical form that has been deformed in one direction from the mean. Morphological disparity is measured as a sum of variance from the mean (Foote, 1993) and in this study is calculated from all relative warps This is a relative metric meant for comparison between groups derived from the same data set Th e most meaningful disparity comparisons are drawn between groups of equal sample size ( Cardini and Elton, 2007) Disparity as calculated from geometric morphometrics has a bias toward the subgroup with the larger sample. Because the mean will be closer to the morphospace of the subgroup, the resulting disparity of the group with the most specimens may be lower. The disparity for each group was measured using the program DisparityBox7 ( Sheets, 2010) T he program requires a different format from the Relative Warps analysis however, so the tps file from tpsDig2 had to first be converted into x y coordinates for each axis of variation. The program C oordGen7a (Sheets, 2011) can
175 convert the landmark data from tpsDig2 into x y coordinate values called X1Y1 format. The formatted file can then be loaded into the program DisparityBox7 The advantage to calculating disparity in this program, as opposed to another method, is that in addition to calculating disparity from the data set, it can also use bootstrap analyses to produce confidence intervals and standard deviation for the disparity values Disparity is calculated by summing variance from the consensus mean across all axes of variation. As a test, I also handcalculated disparity directly from the relative warps data for one of the data sets and found identical disparity values to the DisparityBox7 program. In order to produce confidence intervals and standard deviations for the disparity values, the program resamples the data and calculates disparity for many repetitions to generate the 95% confidence interval As a result subsets with low sample size like Dyrosauridae, will inevitably have wider confidence intervals than subsets with higher samples sizes like Crocodylia. In addition to the larger crocodylian da ta set, four species were selected to construct ontogenetic morphospace ( Alligator mississippiensis Caiman crocodilus Crocodylus niloticus and Crocodylus porosus ). Ages of the specimens are unknown and a proxy was needed. Dorsal skull length was used as a proxy for age. An individual tps file was generated for each of the species and dorsal skull length was tested for correlation against the relative warp axes. Except for one portion of the ontogenetic study, these analyses did not utilize any size const raints, and all morphospace plots were generated irrespective of overall size. Only shape and structure were analyzed because skull size was not a component of the study. As such, landmarks for small and large skulls were aligned and analyzed equally
176 Only because a proxy was needed for age was size utilized in the ontogenetic component of the study. Within morphospace, i f large individuals plot differently than small ones, it is due to a difference in shape, not size. Results R elative W arps analysis of al l living species of adult crocodylians (n=209) was conducted (Fig 5 2). The occupation of morphospace was similar between this study and previous studies of extant crocodylian morphospace (Pierce et al., 2008; Sadleir, 2009; Pearcy and Wijtten, 2011). Mor phospace occupation was particularly similar for Gavialis which had a clear offset from all other extant crocodylia when the first two axes were compared, and a small amount of overlap when comparing the axes separately (Pierce et al., 2008; Sadleir, 2009) A separate analysis was conducted using just Dyrosauridae (n=10; Fig. 53). The Cerrejn dyrosaurids make a large contribution to the overall morphospace of Dyrosauridae. When the dyrosaurid and crocodylian data sets were combined and a new relative war ps file generated, a more meaningful comparison can be drawn between the two (Fig. 54). In this combined morphospace analysis dyrosaurids exhibited wider morphospace occupation than all extant crocodylia within the data set particularly with respect to Relative Warp 1 and possessed a clear offset from all but Gavialis with respect to Relative Warp 2 (Fig. 55 ) The first two relative warps accounted for 62.35% of variance (Table 51). Relative warps analyses were run on each of the four species study set s isolated for ontogenetic study The first relative warp, mostly variation in snout length, was compared to dorsal skull length, a proxy for age. Each of these comparisons resulted in statistically significant correlation between relative warp 1 and dorsa l skull length (Table
177 5 2; Fig. 5 6 ). When the four study sets were plotted within morphospace alongside Dyrosauridae (Fig. 57 ), a similar shift wa s apparent from young individuals to adults. Values for Crocodylus porosus are less clearly distinguished be tween young and adults, but may be due to the confounding effects of adding the second relative warp (RW2) data that are less correlated with age than for the other three species. D isparity results as determined by DisparityBox7, the sum of all variance, w ere 0.0221 for Dyrosauridae and 0.0083 for all extant Crocodylia (Table 53 ). Measured disparity is thus 2.65 times higher in the Dyrosauridae relative to all living crocodylians A bootstrap analysis was conducted on the resulting disparity for this data set using 1,600 reptitions. The 95% confidence intervals are wide for Dyrosauridae ( n=10; lower: 0.0058 ; upper: 0.0346) and much narrower for extant Crocodylia (n = 209; lower: 0.0071; upper: 0.0098). The overlap of the crocodylian confidence interval repres ents 9.4% of the overall confidence interval of Dyrosauridae. When broadened out to the lower limit of the dyrosaurid confidence interval there would be a 13.9% chance that resampling of Dyrosauridae would result in disparity equal to or lower than extant crocodylia. The fact remains that measured dyrosaurid disparity was much higher than the extant crocodylian sample in the current analysis and resampling of Crocodylia did not result in greater disparity than 86.1% of the confidence interval for Dyrosauridae. The bias is still present between the very different sample sizes of Dyrosauridae and Crocodylia. Due to the constraints of sampling fossil taxa for which few skulls are known, Dyrosauridae was in effect reduced to a single representation per species w ithin the morphospace analysis As each dyrosaurid specimen in the data set represents an ideal form of the species (without preservational gaps in morphology ) it seemed relevant to
178 sample the extant subset likewise. I selected an ideal adult representativ e for each species within the extant subset and reran the disparity analyses Disparity for Dyrosauridae was virtually unchanged (0.02214694) but extant crocodylia was a little higher (0.01159916). Instead of a difference of 2.65 betweent the two groups, disparity was 1.9 times higher in Dyrosauridae. The sample size of Crocodylia reduced from 209 to 24 (an 88.5% decrease) and the difference in disparity was 28.3% less. The difference in sample size of Dyrosauridae to Crocodylia was 4.7% with the larger dat a set and 41.7% with the smaller data set. Sample size is still not equal between the two study groups, but further subsampling of extant crocodylia would itself introduce an additional bias to the analysis. The tps file generated with exclusively Dyrosaur idae was used to calculate relative disparity for the group through time. Sample sizes are necessarily even lower for these subsets of the dyrosaurid population, however they are closer to equal in size. When comparin g the geologic stages through time in m orphospace, there is a steady expansion and contraction, when looking at the first two relative warps (Fig. 58 ). Morphospace is necessarily small whenever only two taxa are included, as in the Maastrichtian when only Chenanisuchus lateroculi and Rhabdognathus keiniensis are known from reasonably complete skulls (Hill et al., 2008) The expansion with Guarinisuchus and At l antosuchus in the Danian enlarges morphospace in these axes The largest morphospace occupation occurs during the Selandian with the incl usion of the Cerrejn taxa. Were this to be restricted to marineonly taxa, the polygon would look much more similar to that of the Danian (Fig. 5 8 ) Morphospace is similar in the Thanetian and Danian, but then notably contracts during the Ypresian. The Y presian
179 stage has only three species within two genera known from reasonably complete skulls Dyrosaurus maghribensis and Dyrosaurus phosphaticus plot extremely close to each other, and thus do not contribute very differently to morphospace. The relative w arps analysis does produce more quantified deviation from the mean with the other warp axes, so it is worthwhile to also look at disparity through time when incorporating all axes (Table 53 ) Using values of relative disparity calculated with the program DisparityBox7, disparity can be quantified through time and confidence intervals produce d (Table 53 ; Fig. 5 9 ). Within marine and brackishwater dyrosaurids, the disparity follows a steady decline from high levels in the Maastrichtian to their lowest lev els in the early Eocene. A slight peak occurs in the Selandian even without the addition of the Cerrejn taxa. The addition of Cerrejonisuchus and Unnamed Taxon results in the largest disparity throughout the groups history. Sample sizes are low for each stage (Table 53 ), and as a result the confidence intervals for each of these values are very broad. There was not a statistically significant correlation between disparity and sample size of dyrosaurids through time (Pearsons pvalue=0.550). Morphospace Discussion The confidence interval overlap between disparity in Crocodylia and Dyrosauridae renders the two groups statistically invalid as significantly different Due to the style of analysis run and the settings utilized, t he comparative shifts between Dyrosauridae and Crocodylia are controlled by shape and skull structure, not size Thus the large size discrepancy between Cerrejonisuchus improcerus and Unnamed Taxon is not factored into this analysis The placement of Cerrejonisuchus improcerus closer t o the rest of Dyrosauridae, and especially given its more longirostrine skull shape, seems
180 to indicate it was closer in overall skull structure to more typical dyrosaurids than Unnamed Taxon. Conversely, Unnamed Taxon appears to fall within anticipated juv enile morphospace despite its large size. Similarity to juvenile dyrosaurids could be corroborated with the discovery of truly juvenile dyrosaurid fossils, but only isolated postcranial elements have been discovered thus far. The three Cerrejn taxa are not likely to be different growth stages of a single taxon, as each is known from multiple individuals with elements that confirm their adult age Moreover, each can reliably be indentified by its own unique suite of characters that diagnose each as its own taxonomic unit. The strong correlation between ontogeny and relative warp 1 in the four sampled species of extant crocodylians is encouraging for understanding the means by which Dyrosauridae attained this disparity in the freshwater environment. Freshwat er habitat has been hypothesized as the typical habitat for young dyrosaurids based on the generally smaller size of the few fragments of dyrosaurid fossils found in freshwater habitats as well as the exclusively adult status of the well sampled, dyrosauri d rich deposits in Morocco (Jouve et al., 2008b). The presence of large adults in the entirely freshwater environment of Cerrejn is unprecedented. The unusual morphology of Unnamed Taxon in particular could be accounted for in part by retention of juvenil e skull shape. Given snouts are proportionally shorter in extant hatchling crocodylians than their adult counterparts ( e.g. Crocodylus porosus ; Webb and Messel, 1978) shorter snouts would be expected in young dyrosaurids. The same shift in extant crocodyl ian morphospace from young to adult is present between adult Cerrejn dyrosaurids and adult marine/ estuarine dyrosaurids. With such small sample sizes these data are far
181 from conclusive, but at least suggest the possibility that the wholly unique morpholog y of Unnamed Taxon was obtained through retention of juvenile traits. Furthermore, the smallest Cerrejn dyrosaurid, Cerrejonisuchus did not plot within the morphospace that is most likely comparable to juvenile status, while the much larger Unnamed Taxon did (Table 41). An ontogenetic study of the broadsnouted caiman, Caiman latirostris resulted in suggestive data for retention of juvenile skull morphology into adulthood resulting in morphology different from its congeners, Caiman crocodilus and Caiman yacare ( Monteiro et al., 1997) Monteiro et al. (1997) hypothesized that retention of juvenile skull morphology was likely useful for durophagy, and indeed C. latirostris has been recorded with hardbodied prey items with in its stomach contents ( Borteiro et al., 2009). A similar pathway may have been followed in Dyrosauridae, explaining the short snouted morphology of the Unnamed Taxon and possibly leading to durophagous diet Diversity Analyses Methods Diversity for Dyrosauridae was compiled from the literature and included all specimens which could be identified at least to genus. As a result this necessarily excludes time periods for which fossils that are only diagnostic to Dyrosauridae have been found. Genus level diversity was obtained from Benson et al. (2010) which compiled number of genera for Sauropterygia and Mosasauroidea based on relevant large scale studies of their relative ingroup evolutions. Diversity for Eocene cetaceans was obtained from Uhen (2010) Shark diversity had not been compiled over the time frame of the study (Late Cretaceous Eocene) so selachiian diversity was determined from the P aleobiology D atabase ( www.paleodb.org ).
182 Th is study has focused on generic diversity (as opposed to species diversity) in order to avoid some of the nomenclature issues that are more prevalent at the species level. Also, this more fully utilizes the less diagnostic fossil record, and allows fossils to be included which could not be identified to species, but could be identified to genus. All lazar u s gen era were ranged through meaning in cases where fossils were recovered from nonconsecutive geologic stages, they were counted as present in the interim This prevents apparent declines in diversity which are really only reflecting lack of sampling and/o r much shorter interim stages with less potential for fossil preservation. Furthermore, in order to occur in a later stage, the genus must have existed. In truth, lazarus taxa may reflect incorrect identification, but a global reevaluation of all marine vertebrate records is far beyond the scope of this study. However, the total number of genera for the foc a l group of this dissertation, Dyrosauridae, has been evaluated with a critical eye for all geologic stages. Another method has been applied to account f or even higher possible diversity levels which apply ghost lineages as implied by phylogenetic studies I did not incorporate this method, as ghost lineages are completely dependent on the topology of the cladograms produced, and change drastically based o n factors such as taxa included and completeness of the fossi ls anal yzed With known wild card taxa within Dyrosauridae alone, such diversity estimates would be very unrelia bl e Also, firm phylogenies have not been produced for all fossil and extant Selachii, and a meaningful comparison could not be made using that method. The first step in adjusting for sampling bias in the marine rock record was to establish the amount of fossiliferous marine formations (FMFs) available for each
183 geologic stage in which fossils could be preserved. These FMFs were obtained from the Paleobiology Database. Diversity and FMF were reranked independently according to increasing number These paired values were then used to determine a linear regression. Th e equation of this regression was then used to calculate the anticipated residual diversity, if sampling were dependent on availability of FMFs for each geologic stage. The idea posed by Benson et al. (2010) is that this residual diversity represents a corrected value for diversi ty that reflects the bias posed by differing quantity of FMFs through time. Geologic time needed to be grouped into practical time bins Most stratigraphic data for fossil localities use geologic stages, more often than absolute ages As absolute dates are rare for fossil localities, I chose to group values by geologic stage. The current study focused on the entire Late Cretaceous through Eocene, as it encompasses the full range of Dyrosauridae as well as geologic stages before and after their existence. Ot her potential sampling biases. Rarefaction can be useful to give a more probable representation of diversity from a sampled population ( Raup, 1975 ) but the method requires identification of specimens from the sampled site to the desired taxonomic level. A s o nly cranial fossils of crocodyliforms are identifiable to genus at Cerrejn, this method is impractical for the present study and rarefaction methods were not applied. Other biases can affect measured diversity such as taxonomy. When some groups are mor e often split into more groups or lumped into larger genera, this can affect the measured diversity and create a bias This can be accounted for by critically evaluating each of the taxonomic records but it is a timeconsuming endeavor for large
184 groups. For this reason, the study focuses on relative diversity between groups living in similar environments more than overall diversity This too can of course be biased, but many of the biasing factors for one group also apply to groups living in the same general habitat Meaningful comparisons can thus still be drawn between the relationships of diversity curves to each other. Results Diversity curves are presented with shaded under line scatter plots (Fig. 510) Points represent values at the median age of g eologic stage. Diversity of sauropterygians and mosasauroids fluctuates in the early Late Cretaceous, but then evens out toward the Maastricthian. Conversely, dyrosaurid diversity steadily increases during the Paleocene, and declines into the Eocene. The decline of dyrosaurids is coeval with the increase of cetacean diversity which increases dramatically after the extinction of Dyrosauridae. Selachian diversity increases coevally with sauropterygian and mosasauroid diversity but falls markedly at the K Pg boundary Selachian diversity increases again toward the end of the Paleocene and into the Eocene, but declines again with the peak in Eocene diversity among Cetaceans. Selachian diversity wa s consistently much higher than any of the other groups throughout th e study period (Fig. 5 10) The residual diversity (Fig. 5 11) of mosasauroids and sauropterygians follow similar trends of peaks and declines through the Late Cretaceous through time as compared with raw diversity. Dyrosaurids reach a large peak in the middle Paleocene, whether or not the Cerrejn taxa are included. Cetacean diversity is low in the Eocene but rises dramatically, much like the raw diversity curve. Selachii were the only group to
185 have correlated so tightly with FMFs that their residual di versity is very consistent, with only a minor decrease at the K Pg boundary Correlation statistics were generated between each of the major taxonomic groups and FMF count and the duration of the geologic stage (Table 54). The correlation between FMF and diversity was statistically insignificant for every group except Selachii The correlation between duration of geologic stage (as determined from Gradstein et al., 200 4 ) was statistically insignificant for all groups except Dyrosauridae However, the correla tion is inverse with or without the Cerrejn dyrosaurids There is a statistically significant inverse correlation between Dyrosauridae and a combined diversity curve for Mosasauroidea, Sauropterygia, and Cetacea (Table 55) Thus, by isolating the comp arison to dyrosaurids and nondyrosaurid tetrapods, it appears that in the absence of large marine reptiles in the Paleocene, dyrosaurids attain peak diversity (with or without the Cerrejn forms). However, with the residual diversity correction, the relat ionship between the two diversity curves is not statistically significant. Diversity Discussion The uncorrected diversity curves suggest the possibility that in the absence of competition from other marine predators, dyrosaurids flourish whether or not the Cerrejn taxa are included (Fig. 5 10). Considering the rise, prevalence, and increased number of species are all greatest during the Paleocene when mosasaur oid s, sauropterygians, and cetaceans were present is suggestive. A correlation has not been propos ed before between these large tetrapod predators Furthermore, as cetaceans spread throughout the localities where dyrosaurids had already been established, they appear to have been more successful in terms of number of genera (Uhen, 2010). Much
186 like the biogeographic analysis of Chapter 4, this method cannot incorporate fossils from geologic stages which do not have dyrosaurid fossils diagnostic to the genus level Dyrosaurids persist into later parts o f the Eocene in Asia (Buffetaut 1978b, 1978c), but are non diagnostic The correlation between FMF and diversity were all insignificant except for selachiians. As a result, comparison of residual diversity curves appeared insignificantly correlated. The reason for an inverse correlation between length of the geologic stage and dyrosaurid diversity is likely coincidental as the opposite would be expected if length of time led to a greater opportunity to fossilize. The measured disparity through time as determined from morphospace showed a steady decline with ei ther a small or large peak in the middle Paleocene depending on whether or not Cerrejn taxa were included. The declining disparity itself may have contributed to the eventual extinction of the dyrosaurids. Even in cases of constant diversity, declining di sparity can be tied to extinction forced by selection. In the case of ammonoids, extinction across different morphologic groups with constant disparity was interpreted as a nonselective, or catastrophic extinction ( Villier and Korn, 2004) In the case of other taxa with declining disparity, these were interpreted as being driven by selective extinction. Such is likely the case for Dyrosauridae, and would indeed be better explained by the associated extinction from increasing competition by cetaceans. Ceta ceans during the early middle Eocene not only radiate in form but disperse widely geographically along a largely Tethyan dispersal (Uhen, 2010). The widespread cetaceans of this time are protocetids and basilosaurids The carnivorous protocetids in particular had very similar habitats in coastal marine environments and most likely were
187 capable of locomotion on land, much like dyrosaurids These early whales lacked adaptations associated with a fully marine lifestyle such as an elongate caudal series and reduced pelvic bones (Uhen, 2010). The coeval basilosaurids would have been more pelagic than the protocetids, but were also widespread carnivores throughout the Tethys and persisted into the late Eocene. Larger sample sizes, particularly for Eocene d yrosauri d s would help improve this test for correlation.
188 Table 51. Percent varianc e for individual relative warps in the adult dyrosaurid and crocodylian relative warp analysis. Relative w arp % Variance 1 48.51% 2 13.84% 3 6.40% 4 5.01% 5 4.47% 6 2.79% 7 2.15% 8 1.85% 9 1.60% 10 1.36% 11 1.30% 12 1.09% 13 0.88% 14 0.82% 15 0.78% 16 0.70% 17 0.55% 18 0.48% 19 0.46% 20 0.45% 21 0.38% 22 0.34% 23 0.33% 24 0.30% 25 0.25% 26 0.22% 27 0.21% 28 0.19% 29 0.18% 30 0.17% 31 0.15% 32 0.13% 3 3 0.12% 34 0.11% 35 0.11% 36 0.10% 37 0.10% 38 0.09% 39 0.08% 40 0.08% 41 0.08% 42 0.07% 43 0.06% 44 0.06% 45 0.05% 46 0.05% 47 0.05% 48 0.04% 49 0.04% 50 0.04% 51 0.04%
189 Table 51 Continued. Relative w arp % Variance 52 0.04% 53 0.03% 54 0.03% 55 0.02% 56 0.02% 57 0.02% 58 0.02% 59 0.02% 60 0.02% 61 0.01% 62 0.01% 63 0.01% 64 0.01% 65 0.01% 66 0.00%
190 Table 52. Correlation statistics for ontogenetic study of four extant crocodylian species. Data set included a total of 109 individual skulls. Genus Species Sample s ize Linear r egression of s kull l ength to RW1 R2 c orrelation Correlation p values Pearsons Spearmans Kendalls Alligator mississippiensis 20 317.66x+32.904 0.6067 <0.0001 <0.0001 <0.0001 Caiman crocodilus 51 137.56x+18.219 0.7826 <0.0001 <0.0001 <0.0001 Crocodylus niloticus 25 306.78x+32.841 0.6225 <0.0001 0.001 <0.0001 Crocodylus porosus 23 356.34x+35.438 0.6393 <0.0001 <0.0001 <0.0001
191 Table 53 Relative disparity values from the geometric morpho metric study from a total of 219 skulls of crocodylians and dyrosaurids. Confidence intervals were generated using b ootstrap analysis with 1600 replicates through the program DisparityBox7 (Sheets, 2010) Group Subset Sample s ize Disparity 95% c onfidence i nterval Standard e rror l ower u pper Adult Crocodylia + Dyrosauridae Adult Crocodylia 209 0.00835531 0.00705158 0.00978565 0.00067669 Dyrosauridae 10 0.02214693 0.00576168 0.03462426 0.00808074 Singles Extant Crocodylia 24 0.01159916 0.00629801 0.0 1636191 0.00273241 Dyrosauridae 10 0.02214694 0.00709648 0.03636442 0.00825278 All Dyrosauridae Maastrichtian 2 0.0220717 0.00000000 0.02207017 0.01102554 Danian 4 0.01482878 0.00127816 0.01512362 0.00381790 Selandian 5 0.03234185 0.00672460 0.05218 635 0.01178239 Thanetian 4 0.01128646 0.00225639 0.01471345 0.003 60623 Ypresian 3 0.00563265 0.00000000 0.00564820 0.00253981 Non Cerrej n 8 0.00881892 0.00404710 0.01125309 0.00183555 Cerrej n Only 2 0.02449192 0.00000000 0.02449192 0.01225578 S elandian No Cerrejn 3 0.01541582 0.00000000 0.01541582 0.00547969
192 Table 54 Diversity values. Dyrosauridae diversity is compiled in this study and limited to occurrences where fossils could be identified at least to genus FMF stands for Fossiliferous Marine Formations. Values are obtained from 1Benson et al., 2010; 2Uhen, 2010; 3Paleobiology Database; 4Gradstein et al., 2004 Taxonomic g roup Generic d iversity Late Cretaceous Paleocene Eocene Cen Tur Con Sant Camp Maas Dan Sel Than Ypres Lut Bart P riab Mosasauroidea 1 4 7 5 6 9 6 0 Sauropterygia 1 2 8 0 1 4 4 0 Mos+Saur 6 15 5 7 13 10 0 Dyrosauridae 0 4 5 8 6 3 0 Cetacea 2 0 3 23 17 11 Selachii 3 not ranged thru 28 9 4 23 40 32 14 0 25 38 39 19 38 Selachii 3 ranged thru 28 24 23 34 44 36 26 25 33 41 32 33 39 FMFs 3 ** 114 87 47 62 146 130 56 10 40 76 65 72 129 Stage Duration (my)4** 6.1 4.2 3.5 2.3 12.9 5.1 3.8 3 2.9 7.2 8.2 3.2 3.3 *likely incorrect **not a diversity value
193 Table 5 5 Pearson c orrelation statistics for diversity curves Pearson pvalue implies significane when the value is below 0.05 (in bold). Pearson R2 value represents correlation relative to complete correlation with a value of 1. Correlation in the right hand column is the Pearsons correlation coefficient for uncorrected diversity, Raw, and Residual Diversity, RD. Abbreviations: Dyro, Dyrosauridae; Dyro( NC ), Non Cerrejon Dyrosauridae; FMF, Fossiliferous Marine Formations; Mosa, Mosasauroidea; Saur, Sauroptery gia. Pearson p value Pearson R2 # r elevant s tages Correlation c oefficient Mosa/FMF 0.184 0.322 7 0.567 Mosa/Duration 0.220 0.282 7 0.531 Saur/FMF 0.233 0.269 7 0.518 Saur/Duration 0.536 0.081 7 0.285 Mosa+Saur/FMF 0.150 0.366 7 0.605 Mosa+Saur/Durat ion 0.307 0.205 7 0.453 Dyro/FMF 0.088 0.473 7 0.688 Dyro/Duration 0.007 0.799 7 0.894 Dyro( NC )/FMF 0.182 0.324 7 0.569 Dyro( NC )/Duration 0.004 0.841 7 0.917 Cetacea/FMF 0.755 0.037 5 0.193 Cetacea/Duration 0.573 0.117 5 0.342 Selachii/FMF 0.028 0.366 13 0.605 Selachii/Duration 0.053 0.299 13 0.547 Dyro/Mosa (Raw) 0.333 0.750 3 0.866 Dyro/Saur (Raw) 0.546 0.429 3 0.655 Dyro/Mosa+Saur (Raw) 0.404 0.648 3 0.805 Dyro/Cetacea (Raw) 0.257 0.846 3 0.920 Dyro/Mosa+Saur+Cetacea (Raw) 0.01 7 0.714 7 0.845 Dyro/Selachii (Raw) 0.099 0.450 7 0.670 Dyro( NC )/Mosa+Saur+Cetacea (Raw) 0.010 0.763 7 0.874 Dyro( NC )/Selachii (Raw) 0.185 0.321 7 0.567 Dyro/Mosa+Saur+Cetacea (RD) 0.817 0.012 7 0.108 Dyro/Selachii (RD) 0.486 0.101 7 0.318 Dyro(NC )/Mosa+Saur+Cetacea (RD) 0.690 0.034 7 0.186 Dyro( NC )/Selachii (RD) 0.547 0.077 7 0.278
194 Figure 51. Diagrams and example used in geometric morphometric study. A) Reconstructions of Unnamed Taxon (left) and Cerrejonisuchus improcerus (right); B) Example of landmarks adapted from Pierce et al., (2008) on modern Crocodylus skull (AMNH R 29294). Scale bar s equal 10 cm.
195 Figure 52 Morphospace x y scatter plot of 209 adult crocodylian skulls resulting from relative warps analysis. X axis is Relat ive Warp 1; Y axis is Relative Warp 2. Thin plate splines are presented at the end of each axis pre sented in the current analysis.
196 Figure 53 Morphospace x y scatter plot of all 10 dyrosaurid taxa known from reasonably complete skulls resulting from r elative warps analysis. X axis is Relative Warp 1; Y axis is Relative Warp 2. Thin plate splines are presented for the four extremes presented at the end of each axis in the current analysis. Cerrejn taxa ( Cerrejonisuchus improcerus and Unnamed Taxon) are highlighted in green.
197 Figure 54 Morphospace x y scatter plot of combined dyrosaurid and extant crocodylian morphospace, totaling 219 specimens. X axis is Relative Warp 1; Y axis is Relative Warp 2. Thin plate splines are presented for the four extrem es presented at the end of each axis in the current analysis.
198 Figure 55 Morphospace x y scatter plot of combined dyrosaurid and extant crocodylian morphospace, totaling 219 specimens. Each group is highlighted separately. X axis is Relative Warp 1; Y axis is Relative Warp 2.
199 Figure 56. Correlation x y scatter plots of four species of extant crocodylia. X axis is Relative Warp 1 and Y axis is dorsal skull length as measured from tip of snout to posterior margin of skull table. For equations of tre ndlines and correlation statistics refer to Table 52. A) values for Alligator mississippiensis B) values for Caiman crocodilus C) values for Crocodylus niloticus D) values for Crocodylus porosus
200 Figure 57. X Y scatter plot of first two relative w arps showing morphospace occupation resulting from combining the ontogenetic study set and Dyrosauridae. Note colors of younger extant individuals are lighter in color than their adult counterparts. In all extant species, the younger individuals are found with higher RW1 and RW2 values. This same condition is seen between the two Cerrejn taxa ( Cerrejonisuchus improcerus and Unnamed Taxon) and all other Dyrosauridae. Abbreviations: A. miss, Alligator mississippiensis ; C. croc, Caiman crocodilus ; C. porosus, Crocodylus porosus ; C. niloticus, Crocodylus niloticus
201 Figure 58 Morphospace x y scatter plots for each geologic stage for Dyrosauridae. X axis is Relative Warp 1; Y axis is Relative Warp 2.
202 Figure 59 Results of disparity analyses generated fr om geometric morphometric study of Dyrosauridae through geologic time binned into stages Purple represents all nonCerrejn dyrosaurids The green addition during the Selandian is the contribution made by the two Cerrejn dyrosaurids.
203 Figure 510. Un corrected generic diversity curves through geologic time. Values presented on right column are number of genera, all of which have been ranged through for lazarus taxa. Bars at the top represent occurrence through geologic time Small arrows indicate the t axon can be found before/after the end of the displayed time frame.
204 Figure 51 1 Residual diversity curves using method of Benson et al. (2010) incorporating bias correction for stages with more fossiliferous marine formations. Data are plotted alongside geologic time, binned in stages. Abbreviation: MO, marine and brackish water only (i.e. nonCerrejn) .
205 CHAPTER 6 CONCLUSION Dyrosaurid Systematics The crocodyliforms of the Cerrej n locality are all diagnosable to Dyrosauridae. W ithin this assemblage are three clearly different morphotypes, each representing a new genus and species of dyrosaurid. Provided in this dissertation are the necessary diagnoses and thorough morphological descriptions that are essential to properly naming new species Holotypes hav e been assigned for each of these species and two are formally recognized as published species Cerrejonisuchus improcerus (Chapter 2) and Acherontisuchus guajiraensis (Chapter 3) The consequence of working in a region and time period that has been poorly sampled is that most taxa found represent wholly new species and genera previously unknown to science. The benefit to such consequences is the opportunity to form the framework of comparison and name the species which may likely be discovered elsewhere. Phylogeny In order to understand the relationships of the new dyrosaurids to other members of the family, a new phylogenetic character set was generated for this dissertation research. This involved modifications of characters used in smaller data sets as well as wholly new characters The phylogenetic results largely agree with past studies of dyrosaurid relationships Chenanisuchus lateroculi from the Paleocene of Africa consistently appears as the most primitive of dyrosaurids. Cerrejonisuchus and Unnamed Taxon appear as the next most primitive forms, but do not appear as sister to each other. These results imply that the primitive condition for Dyrosauridae counter intuitively is short snouted and that longirostry is actually a derived trait within the f amily.
206 Placement of Acherontisuchus guajiraensis is problematic due to the mix of primitive and derived characters within the taxon and its low amount of codable characters rendering it a wildcard within the phylogenetic analysis Outwardly, A. guajiraens is appears most similar to the longirostrine forms Hyposaurus and Guarinisuchus of the New World. However, without more complete material it will be not be possible to obt ain a more definitive position with the current matrix It is possible an expanded matrix incorporating postcrania could aid in a more resolved relationship, but such a study would be limited to the few dyrosaurid taxa for which postcrania are associated with identifiable skulls. Biogeography The further benefit of phylogenetic studies is the biogeographic implications that can be drawn from them When geography and age are incorporated into topology, timing of dispersal events can be discerned. Combining past continental placement, ocean circulations, and sea surface temperatures can be used to determine likely dispersal routes to explain the fossil taxons appearance by a certain time at a certain place. The most primitive member of Dyrosauridae is consistently Chenanisuchus of Africa This species is also known from the oldest dyrosauridbearing deposits (at least those that can be identified to species) thus retaining the origin of the family within Africa Pholidosauridae, t he outgroup typically regarded as ancestral to Dyrosauridae ( Jouve et al., 2006), is largely known from Africa. T here appears to have been a very early dyrosaurid dispersal from Africa to the New World shortly after the groups earliest occurence in the Late Cretaceous, ultimately giving rise to dyrosaurids in Colombia. The dyrosaurids would likely have continued dis persal along the ancient coast of the present
207 day Gulf of Mexico, following the early components forming what is now Central America, and ultimately reaching the eastern shores of the modern day United States F ossils of the dyrosaurid Hyposaurus rogersii can be found from the Late Cretaceous through Paleocene deposits across the ancient Atlantic seaboard of the United States A new Cretaceous dyrosaurid fossil from Mexico serves to corroborate this hypothesis ( Shiller, 2012). In all three independent disp ersals across the early Atlantic Ocean are apparent These dispersals follow ocean cir culation patter n s as well as portions of these circulatory patterns that are the warmest. This implies though that the Cerrejn ancestors were marine in habitat and capa b le of navigating large expanses of open water. Evidence from modern saltwater croc o diles has shown these crocodylians will utilize wave motion in order to conserve energy and cross great distances ( Campbell, 2010). Paleobiology Fossil crocodyliform literat ure is very often highly focused on cranial morphology The common reason for this has been an understanding that postcranially, crocodyliforms have been morphologically conservative. However, even with the few fragmentary bones of the skeleton of Cerrejn dyrosaurids, there have been discernible and functionally important differences between them and other members of the family. Each morphotype represents a different ecological niche. The dwarf species, Cerrejonisuchus improcerus would have predated on li zards, frogs, small fish, and invertebrates, taking advantage of the smaller prey items available at Cerrejn. The long snouted species, Acherontisuchus guajiraensis would have specialized on catching fish, with its long narrow jaws being beneficial for c atching quick moving osteichthyans. Both lungfish and elopomorph fossils have been found at Cerrejn and
208 were likely prey for the longirostrine dyrosaurid. The short snouted Unnamed Taxon seems to have had adaptations for testudine predation, with blunt powerful jaws and strong robust teeth. Morphospace a nd Diversity The contributions of the Cerrejn taxa to morphospace more than doubled the overall disparity of Dyrosauridae. This group was clearly able to take advantage of a new habitat and diversify Cont inued research in northern South America will likely discover more occurences of dyrosaurids perhaps even filling entirely different niches. The dyrosaurids 40 million year tenure attained its peak by all accounts in the middle Paleocene. New discoveries may begin to flesh this out and create a fuller appreciation of this once cosmopolitan lineage. Concluding Remarks The fauna of the warm Paleocene Epoch is an indicator for times of diversification for at least one line of crocodyliform evolution. During this particularly warm period in earths past (Head et al., 2009) it appears crocodyliforms can be very successful The warm temperatures of the middle Paleocene certainliy contributed to large body size in the cohabitant of Cerrejn, Titanoboa cerrejonens is (Head et al., 2009) This climate may also at least in part explain the reason for dyrosaurids to have had the ability to become so diverse. Selective pressures may have been relaxed in cases like Cerrejn where ambient temperature was high, allowing dyrosaurids to be successful despite living alongside a 13 m boid snake. The Cerrejn crocodyliforms have shown that even alongside a much larger predator, they can diversify in habitat, form, and function These discoveries may very well be borne out agai n in the near future in areas where crocodylians currently inhabit.
209 APPENDIX A CLADISTIC ANALYSIS CHARACTER LIST Description of characters used in phylogenetic analyses. Outgroup consists of Sarcosuchus imperator Terminonaris robusta, and Elosuchus cheri fensis Ordered characters are labeled as such; all other characters are unordered. Except where otherwise stated, characters are original to this publication. Characters which have been modified from other publications are cited with the character number in bold after the citation. General (1) Length of snout: greater than 68% (0); lesser than 68% (1) of total skull length, measured from tip of snout to posterior margin of parietal. Modified from Jouve, 2005 5 Cranial Openings (2) Medial tubercles of external nares on the posterior margin: absent (0); dorsal (1); ventral (2). (3) Thickness of anterior margin of external nares: less than half anteroposterior length (0); greater than half anteroposterior length (1). (4) Orbits positioned: medially (0); later ally (1). (5) Lateral margin of the orbit comprised dominantly by: lacrimal (0); jugal (1). (6) Supratemporal fenestrae length and width: subequal or wider than long (0); longer than wide (1). Modified from: Clark, 1994 68; Ortega et al., 2000 41 ; Wu et al ., 2001 67; Sereno et al., 2003 4 ; Jouve et al., 2005b 15; Jouve et al., 2006 12; Jouve et al., 2008 15
210 (7) Interfenestral bar: wide (0); narrow (1). Modified from: Clark, 1994 33 ; Wu et al., 2001 33 ; Sereno et al., 2001 26 ; Jouve, 2005 10; Jouve et al., 2005b 18; Jouve et al., 2006 90 ; Jouve et al., 2008 18 (8) Interfenestral bar: ornamented (0); unornamented (1). Modified from: Jouve et al., 2005b 30 ; Jouve et al., 2008 30 (9) Cross section of interfenestral bar: square shaped (0); shaped as an upright T (1); upsidedown V shaped, in the form of a sagittal crest (2). Following Figure 8 of Jouve et al., 2005a. (10) Posterior walls of supratemporal fenestrae: almost vertical and barely visible in dorsal view (0); dorsally inclined and largely visible in dorsal view (1). Modified from: Jouve et al., 2005b 10 ; Jouve, 2005 6 ; Jouve et al., 2008 10 (11) Lateral arches of supratemporal fenestrae: thick (0); thin (1). Modified from: Jouve et al., 2005b 16 ; Jouve et al., 2008 16 (12) Suborbital fenestrae anteri orly reach: posterior to the anterior 2/3 of the maxillary alveoli count (0); anterior/proximal to the anterior 2/3 (1). Premaxillae (13) Posterodorsal processes of premaxillae reach: proximal or distal to the third maxillary alveolus (0); proximal or anterior to second alveolus (1). (14) Lateral expansion of the premaxillae anterior to premaxillary maxillary suture: present (0); absent (1). (15) Premaxillae: possess 5 or more alveoli (0); possess 4 alveoli (1). Modified from: Gasparini et al., 1991 5 ; Orte ga et al., 2000 133 ; Jouve, 2005 12; Jouve et al., 2005b 26 ; Jouve et al., 2006 182 ; Jouve et al., 2008 26.
211 (16) Third premaxillary alveoli: not enlarged relative to both second and fourth premaxillary alveoli (0); third alveoli enlarged relative to both adjacent alveoli (1). (17) Fourth premaxillary alveolus: enlarged or similar in size to first and second alveoli (0); reduced relative to all other premaxillary alveoli (1). (18) First notch for mandibular occlusion: similar in size to adjacent occlusal spacing (0); significantly larger than adjacent spacing (1). (19) Left and right first premaxillary alveoli: similar or wider interalveolar space than adjacent spacing (0); first premaxillary teeth closely spaced (1). (20) Last premaxillary alveoli position: anterolateral to first maxillary tooth (0); anterior to first maxillary tooth (1). Modified from: Sereno et al., 2001 70 ; Jouve et al., 2006 193. (21) Anteroventral expansion of premaxillae: present (0); absent (1). (22) Premaxillary length as compared to width: slightly longer than wide (0); nearly three times longer than wide or more than three times longer than wide (1). Modified from Jouve et al., 2008 41 Maxillae (23) Margins of maxillae: not linear (0); linear for anterior 2/3 or less (1); linear for over the anterior 2/3 (2). (24) Lateral expansion of maxillae: absent, lateral margins linear (0); present, lateral margins festooned (1). Modified from Jouve et al., 2008 40. (25) Alveolar walls: raised relative to ventral surface of the maxillae in lateral view (0); walls level with this surface (1).
212 (26) Each maxilla possesses: 18 or greater alveoli (0); 1517 alveoli (1); 1014 alveoli (2). Modified from: Gasparini et al., 1991 6 ; Ortega et al., 2000 164 ; Sereno et al., 2001 51; Jouve et al., 2006 18 3 ; Ordered. (27) Maxillary alveoli posterior to anterior margin of orbits: absent (0); present (1). (28) Posteriormost contact between maxillae and palatines on ventral surface relative to posteriormost maxillary alveoli: posterior (0); or anterior (1). (2 9) Maxillae extend posteriorly to: anterior or proximal to level of postorbital bars (0); even with the anteroposterior midlength of supratemporal fenestrae (1); proximal to the level of the posterior margins of the supratemporal fenestrae (2); Ordered. (3 0) Posteriormost alveolus: proximal to level of anterior margin of orbit (0); posterior margin of orbit (1); proximal/posterior to anteroposterior midlength of supratemporal fenestrae (2); Ordered. (31) Maxillary tooth size: variable (0); homodont (1). Modified from: Jouve et al., 2005b 25; Jouve et al., 2008 25. Nasals (32) Nasal in adult form: unfused (0); fused anteriorly (1); entirely fused (2); Ordered. (33) Anteromost extension of the nasal relative to level of first maxillary tooth: posterior (0); an terior (1). Modified from Jouve et al., 2008 42. Lacrimal (34) Lacrimal extends anteriorly: only to posterior 1/3 maxillary alveoli (0); to anterior 2/3 alveoli (1).
213 (35) Lacrimal nasal contact relative to prefrontal nasal contact in adult form: about equal (0); about twice as long (1). Modified from Jouve et al., 2005b 12 ; Jouve et al., 2008 12. (36) Posteromost lateral contact of the maxillary and lacrimal bones as seen in dorsal view: proximal to posterolateral corner of orbits (0); proximal to anterolat eral corner of orbits (1). Frontal (37) Interorbital space, including prefrontals if applicable: narrow, less wide than minimal width of snout, at level of premaxillary maxillary suture (0); broad, wider than minimal width of snout (1). Modified from: Clar k, 1994 20, Wu et al., 2001 20 and Jouve et al., 2005b 22 ; Jouve et al., 2006 83 ; Jouve et al., 2008 22 (38) Anterior frontal extension position: posteriorly located, level with or slightly anterior to the prefrontal (0); very anterior to the prefrontal (1). Modified from Jouve et al., 2008 31 (39) Frontal contribution to interfenestral bar: less than onethird (0); greater than or equal to onethird (1). Modified from: Clark, 1994 23; Sereno et al., 2001 20 Parietal (40) Frontoparietal suture on the interfenestral bar: straight/smooth (0); zigzag (1). (41) Parietal quadrate suture relative to the skull table: vertical (0); parallel (1). (42) Posterodorsal margin of parietal: transversely oriented (0); indented anteriorly (1). Modified from: Jouve, 2005 7 ; Jouve et al., 2005b 11 ; Jouve et al., 2008 11 (43) Medial parietal crest, visible in occipital view: present (0); absent (1).
214 (44) Parietal in occipital view: W shaped (0); concave (1). Modified from Jouve et al., 2008 32 (45) Dorsal portion of pari etal: strongly ornamented with deep pits (0); smooth (1); slightly ornamented (2). Modified from Jouve et al., 2005b 27 ; Jouve et al., 2008 27 (46) Posterior lamina of posterior margin of skull roof above posttemporal fenestrae and the occipital tuberosit ies which overhangs, hiding part of the occipital tuberosity from dorsal view: absent (0); present (1). Modified from Jouve et al., 2008 34 Postorbital (47) Anterolateral process: absent/small (0); pronounced and reaches dorsal margin of jugal (1). Modif ied from: Clark, 1994 28; Ortega et al., 2000 32 ; Wu et al., 2001 28 ; Sereno et al., 2001 24 ; Jouve, 2005 4 ; Jouve et al., 2005b 9 ; Jouve et al., 2006 58; Jouve et al., 2008 9 Squamosal (48) Posterior margin of squamosal lateral to occipital tuberosity: s traight (0); anteriorly concave (1). From: Jouve et al., 2005b 29 ; Jouve et al., 2008, 29 Jugal (49) Ventral portion of postorbital bar: medially displaced with ridge separating postorbital bar from lateral surface of jugal (0); medially displaced from lateral surface of jugal with no ridge (1); nearly flush with lateral surface of jugal (2). Modified from: Ortega et al., 2000 34; Jouve et al., 2006 72. (50) Postorbital bar: nearly vertical (0); slightly anterodorsally inclined (1); strongly anterodorsally inclined (2). From Jouve et al., 2008 35 Supraoccipital
215 (51) Supraoccipital participation to posttemporal fenestrae: present (0); absent (1). Exoccipitals (52) Exoccipital participation to occipital condyle: slight (0); large (1). Modified from: Jouve, 2004 96; Jouve et al., 2005b 5 ; Jouve et al., 2006 104 ; Jouve et al., 2008 5 (53) Occipital tuberosities: absent (0); small and reduced (1); strongly developed (2); Ordered. Modified from: Jouve, 2005 1 ; Jouve et al., 2005b 3 ; Jouve et al., 2008 3 Basisph enoid (54) Basisphenoid rostrum: short (0); extremely long anteriorly (1). From: Jouve, 2005 2 ; Jouve et al., 2005b 7 ; Jouve et al., 2008 7 Basioccipital (55) Single wide ventral rugosity of basioccipital medial to basioccipital tubera: absent (0); presen t (1). (56) Basioccipital tubera in ventral view: oblong (0); V shaped/tear drop shaped (1). (57) Paired grooves along ventral surface, extending from base of occipital condyle to basioccipital tubera: absent (0); present (1). (58) Lateral eustachian foram en: level with medial eustachian foramen (0); dorsolateral to medial eustachian foramen, largely hidden from occipital view by the basioccipital (1). Modified from Jouve et al., 2006 145 (59) Ventral part of basioccipital: vertical, largely visible in occ ipital view (0); strongly inclined, weakly visible in occipital view (1). From: Jouve et al., 2005b 13 ; Jouve et al., 2008 13 Quadratojugals
216 (60) Extension of quadratojugal to cranial condyle for articulation with jaw: does not extend (0); extends largely (1). From: Jouve et al., 2005b 19 ; Jouve et al., 2008 19 Palatines (61) Extension of the palatines to choanae: anterior margin or not (0); antermedial margin (1). From: Jouve et al., 2005b 4 ; Jouve et al., 2008 4 Pterygoids (62) Anteromost point of post erior margin of pterygoidian wing: far anterior to medial eustachian foramen (0) about level with medial eustachian foramen (1). Modified from: Jouve, 2005 8 ; Jouve et al., 2005b 14 ; Jouve et al., 2008 14 Laterosphenoids (63) Laterosphenoid sutures with parietal: parallel to skull table (0); descends posteriorly relative to the skull table (1). Mandible (64) Size of second mandibular alveoli relative to first mandibular alveoli: similar in size (0); reduced in size relative to both adjacent alveoli (1). (6 5) Interalveolar space between second and third mandibular alveoli relative to that of first and second: roughly equal in proportion (0); greater (1). (66) Third mandibular alveoli placement: interalveolar space is roughly equal to that between second and third mandibular alveoli (0); close to mandibular fourth (1). (67) Fourth alveolus in proportion to other mandibular alveoli: enlarged (0); similar in size (1). (68) Fourth alveolar wall: level with adjacent alveoli (0); raised relative to adjacent alveoli (1).
217 (69) First alveolus: directed entirely dorsal (0); slants anteriorly as well as dorsally (1). (70) Anterior portion of mandible: typically exhibits expansion (0); exhibits straight margins without significant lateral expansion (1). Modified from Sere no et al., 2001 72. (71) Point at which mandibular symphysis ends posteriorly: anterior to anterior alveoli (0); posterior to anterior alveoli (1). (72) Occlusal pits for maxillary occlusion: minimal (0); prolific (1). (73) Seventh alveolus: comparable in size to adjacent alveoli (0); reduced in size and close to eighth alveolus (1). Modified from: Jouve, 2004 153 ; Jouve, 2005 3 ; Jouve et al., 2005b 8 ; Jouve et al., 2006 164 ; Jouve et al., 2008 8 (74) Symphysis: wider than high (0); about as wide as hi gh (1). From: Jouve et al., 2005b 17 ; Jouve et al., 2008 17 (75) Retroarticular process: short (0); extremely long and posterodorsally curved (1). From: Jouve et al., 2005b 1 ; Jouve et al., 2008 1 (76) Posteromedial wing of retroarticular process: dorsal ly situated or at midheight (0); ventral on the retroarticular process (1). From: Jouve et al., 2005b 2 ; Jouve et al., 2008 2 (77) Coronoid: present (0); absent (1). From: Jouve et al., 2005b 6 ; Jouve et al., 2008 6 (78) External mandibular fenestra: absent or reduced to a thin slot (0); wide (1). Modified from: Jouve et al., 2005b 20; Jouve et al., 2008 20. (79) Posterior process of angular relative to posterior extremity of the retroarticular process: reaches process (0); remains far anterior (1). From : Jouve et al., 2008 39. Dentition
218 (80) Teeth: robust with very wide alveoli (0); thin, long teeth (1). From: Jouve, 2005 11; Jouve et al., 2005b 21 ; Jouve et al., 2008 21 (81) Distance between teeth from middle of maxilla or mandibular symphysis: nearly constant (0) much longer than in anterior portion of maxilla or mandibular symphysis (1). From Jouve et al., 2008 43 Postcrania (82) Lateral margin of medial dorsal osteoderms: linear (0); serrated and curved, sutured with the lateral osteoderm (sends an acute process laterally) (1). From Jouve et al., 2008 37
219 APPENDIX B CHARACTER MATRIX FOR DYROSAURID CLADISTIC ANALYSIS Table B 1. Character taxon matrix for first 28 characters used in phylogenetic analyses of Dyrosauridae. Outgroup consists of Sarcosuc hus imperator Elosuchus cherifiensis and Terminonaris robusta. Appendix A provides character descriptions. 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 Sarcosuchus imperator 0 0 0 0 0 0 0 0 ? 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminonaris robusta 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 1 0 0 0 0 1 Elosuchus cherifiensis 0 ? 0 0 1 0 0 0 ? 0 0 1 1 0 0 0 0 1 0 0 ? 0 0 1 ? 0 0 1 Arambourgisuchus khouribgaensis 0 ? ? 0 0/1 1 1 1 2 1 ? 0 0 0 1 1 1 1 ? 1 1 1 1 0 0 1 1 1 Hyposaurus rogersii 1 ? 0 0 1 1 1 1 ? 1 1 ? ? 0 1 ? ? ? ? 1 1 ? 1 0 1 2 1 ? Rhabdognathus keiniensis 0 ? ? 0 ? 1 1 1 2 1 1 ? ? ? ? ? ? ? ? ? ? ? 2 0 ? 0 1 1 Rhabdognathus aslerensis ? ? ? 0 1 1 1 1 2 1 1 ? ? ? ? ? ? ? ? ? ? ? 1/2 0 1 ? 1 1 Dyrosaurus phosphaticus 0 1 0 0 1 1 1 0 1 1 1 0 0 0 1 1 0 1 1 1 1 1 2 0 0 0 1 1 Dyrosaurus maghribensis 0 ? ? 0 1 1 1 0 1 1 1 0 0 0 1 1 0 1 1 1 1 1 2 0 0 0 1 1 Chenanisuchus lateroculi 1 ? 1 1 1 1 0 0 0 0 1 ? 0 1 1 ? ? ? 1 ? 1 0 0 0 ? 2 1 ? Sokotosuchus ianwilsoni 1 1 1 0 ? 1 1 1 ? 0 1 ? ? 0 1 1 ? 1 1 1 1 0 0 1 ? 2 1 ? Phosphatosaurus gavialoides 1 1 1 0 1 1 1 1 ? 1 1 1 1 0 1 1 1 1 1 1 1 0 0 1 1 1 1 1 Congosaurus bequaerti 1 1 1 0 1 ? ? ? ? ? ? 0 0 1 1 1 0 1 1 ? 1 1 2 0 0 1 ? ?
220 Table B 1. Continued. 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 Atlantosuchus coupatezi 0 ? ? 0 0 1 1 1 1 ? 1 ? ? ? ? ? ? ? ? ? ? 1 2 0 ? ? ? ? Guarinisuchus munizi 0 1 0 0 0 1 1 1 2 1 1 0 ? 0 1 1 0 1 1 1 1 ? 2 0 1 2 1 1 Cerrejonisuchus improcerus 1 2 0 0 0 1 0 0 0 1 0 0 1 1 1 1 1 1 1 1 1 0 1 0 0 2 1 1 Acherontisuchus guajiraensis 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 2 0 1 ? ? ? Unnamed Taxon 1 1 0 1 0 1 0 0 1 0 0 ? 1 1 ? ? ? 1 ? 1 1 0 1 0 0 1/2 1 1
221 Table B 2. Character taxon matrix for characters 29 54 used in phylogenetic analyses of Dyrosauridae. Outgroup consists of Sarcosuchus imperator Elosuchus cherifiensi s, and Terminonaris robusta. Appendix A provides character descriptions. 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 Sarcosuchus imperator 0 0 0 0 0 0 0 0 0 0 0 ? ? 0 0 ? 0 0 0 0 0 0 ? 0 0 0 Terminonaris robusta 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 ? 0 0 0 0 0 0 ? 0 0 ? Elosuchus cherifiensis 0 0 0 0 1 0 0 1 1 0 0 ? ? 0 1 0 0 0 0 0 0 0 0 0 0 0 Arambourgisuchus khouribgaensis 1 2 1 2 0 1 1 0 ? 0 0 1 1 0 0 1 1 0 1 1 1 ? 0 1 2 ? Hyposaurus rogersii ? ? 1 ? ? ? ? ? ? 1 ? ? ? 1 ? ? 0 0 1 0 1 2 ? 1 2 ? Rhabdognathus keiniensis ? ? 1 1/2 ? ? ? ? ? 1 1 1 1 1 1 1 2 1 1 1 ? 2 ? 1 2 ? Rhabdognathus aslerensis 1 2 ? 0/1 ? ? 0 1 ? 1 1 ? ? 1 1 1 2 1 1 1 2 2 1 1 2 1 Dyrosaurus phosphaticus 1 1 1 2 0 0 0 1 0 0 0 1 1 0 0 0 0 0 1 0 1 1 0 1 2 1 Dyrosaurus maghribensis 1 1 1 2 0 0 0 1 0 0 0 1 ? 0 0 0 2 0 1 0 1 1 0 1 2 1 Chenanisuchus lateroculi ? ? 1 1 1 ? 0 1 1 0 1 1 0 0 1 1 0 0 0 0 0 1 ? 1 1 ? Sokotosuchus ianwilsoni ? ? 0 0 1 ? ? ? ? ? ? ? ? 0 ? ? 0 0 0 0 ? 1 ? ? 1 ? Phosphatosaurus gavialoides 1 2 0 2 1 1 ? 0 ? 0 0 ? ? 0 ? ? 0 0 ? 0 ? 1 ? ? ? ? Congosaurus bequaerti ? ? 1 2 0 ? 1 ? ? 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Atlantosuchus coupatezi ? ? 1 0 0 ? 1 1 0 0 0 1 ? 1 1 0 2 1 ? 1 ? ? ? 1 2 ? Guarinisuchus munizi 1 2 1 0/1 ? 1 0 1 0 0 ? ? ? 1 ? ? 2 ? 1 1 ? 2 ? 1 2 ? Cerrejonisuchus improcerus 2 2 1 2 1 1 ? 0 0 1 0 0 1 0 0 1 2 1 1 0 1 ? 1 1 2 ? Acherontisuchus guajiraensis ? ? 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Unnamed Taxon 0/1 0/1 0 0 1 ? ? 0 0 0 1 0 ? 0 1 ? 2 0 1 0 ? ? ? 1 2 ?
222 Table B 3 Character taxon matrix for characters 55 82 used in phylogenetic analyses of Dyrosauridae. Outgroup consists of Sarcosuchus imperator Elosuchus cherifiensis and Terminonaris robusta. Appendix A provides character descriptions. 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 8 8 8 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 Sarcosuchus imperator ? ? ? 0 0 0 0 0 ? 0 0 0 0 0 0 0 ? 0 0 0 0 0 0 0 0 0 0 0 Terminonaris robusta 0 ? 0 0 0 0 0 1 0 0 1 0 1 0 1 0 0 1 0 0 ? ? ? 0 0 1 0 0 Elosuchus cherifiensis 0 0 0 1 0 0 1 1 ? 0 0 0 0 ? 1 0 0 0 0 0 0 ? ? 1 0 0 1 0 Arambourgisuchus khouribgaensis 1 1 ? ? 0 1 1 1 0 1 1 1 0 1 ? 1 ? 1 1 1 ? ? ? ? ? 1 0 ? Hyposaurus rogersii ? ? 0 ? 1 1 1 0 ? 1 1 1 0 ? 1 1 1 0 1 1 1 1 1 1 0 1 1 1 Rhabdognathus keiniensis 1 1 ? 1 1 1 ? ? 0 ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? 1 1 ? Rhabdognathus aslerensis 1 1 1 1 1 1 1 1 ? ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? 1 1 ? Dyrosaurus phosphaticus 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 1 ? ? 1 1 1 1 ? 0 ? 1 0 0 Dyrosaurus maghribensis 1 1 ? 1 0 1 1 1 1 1 1 1 0 ? 1 ? 1 ? 1 0 1 1 1 0 1 1 0 0 Chenanisuchus lateroculi 1 ? ? ? 0 1 ? ? 0 ? ? ? ? ? ? ? ? ? ? 0 1 1 ? ? ? 1 0 ? Sokotosuchus ianwilsoni ? ? ? ? 0 ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? 0 0 ? Phosphatosaurus gavialoides ? ? ? ? 0 ? 1 1 ? ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? 0 0 ? Congosaurus bequaerti ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 ? ? 1 ? 1 1 1 0 0 1 1 1 Atlantosuchus coupatezi ? ? ? ? ? 1 ? ? ? 0 1 1 1 0 1 1 ? ? 1 1 1 ? ? ? 1 1 1 ? Gu arinisuchus munizi ? 1 ? ? 1 1 1 ? ? ? ? ? ? ? ? ? ? 1 ? 0 ? ? ? ? ? 1 ? ? Cerrejonisuchus improcerus 1 1 0 1 ? 1 ? ? 0 1 1 1 0 1 1 1 0 0 1 ? ? ? ? ? ? 1 ? ? Acherontisuchus guajiraensis ? ? ? ? ? ? ? ? ? ? ? ? 0 0 ? ? 1 0 1 0 ? 1 ? 0 ? 1 0 ? Unnamed Ta xon ? ? 0 ? ? 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 ? 0 ? ?
223 APPENDIX C CHARACTER MATRIX FOR CROCODYLOMORPH CLADISTIC ANALYSIS Cladistic data for Unnamed Taxon and Cerrejonisuchus improcerus used in the analysis by Jouve et al. ( 2006). A total of 234 characters were coded and the other 47 taxa used in the previous analysis remain unchanged.
224 Table C 1. Coded character states for characters 1 30. 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon 1 0 ? 0 2/3 0 0 1 1 3 0 1 0 ? ? ? ? ? ? ? ? ? ? ? 1 1 0 1 1 3 Cerrejonisuchus improcerus 1 0 ? 0 2 0 0 1 1 3 0 1 1 0 1 1 ? ? ? ? ? ? ? 0 1 1 0 1 1 3 Table C 2. Coded character states for characters 31 60. 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 6 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon 0 1 0 0 0 2 0 0 ? 0 0 0 0 0 1 2 0 1 1 0 1 1 ? ? 0 ? ? 1 ? ? Cerrejonisuchus improcerus 0 1 0 0 0 2 0 0 ? 0 0 0 0 0 1 2 0 1 1 0 1 1 ? ? 0 ? ? 1 ? ? Table C 3. Coded character states for characters 61 90. 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 9 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon ? 1 1 0 2 ? 0 1 ? 0 ? ? 0 ? ? ? ? 0 ? ? ? 0 1 0 1 0 1 0 0 Cerrejonisuchus improcerus ? 1 1 0 2 ? 0 1 ? 0 1 ? 0 ? ? 0 0 0 1 0 ? 0 1 0 1 1 1 0 0 Table C 4. Coded character states for characters 91 120. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon 0 1 ? 1 1 ? ? 0 ? 1 0 ? ? 1 ? ? ? 1 1 2 2 ? 0 0 0 0 ? ? 0 ? Cerrejonisuchus improcerus 0 1 1 1 1 0 1 0 0 1 0 ? ? 1 0 ? ? 1 1 1 2 0 0 0 0 0 ? ? ? ? Table C 5. Coded charac ter states for characters 121 150 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon 0 1 1 ? 0 0 1 0 0 ? 1 ? ? ? ? ? ? ? 0 ? 0 0 1 1 ? ? ? 1 ? ? Cerrejonisuchus improcerus ? ? ? ? ? ? ? ? 0 ? 1 1 ? ? ? 2 1 0 0 0 0 0 1 ? ? ? ? ? ? 1 Table C 6. Coded character states for characters 151 180 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 5 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 8 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon ? ? 0 ? 1 ? 0 0 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Cerrejonisuchus improcerus 0 1 0 1 1 ? ? ? ? ? 1 ? 0 1 ? ? ? ? ? ? ? 2 ? ? ? ? ? ? ? ? Table C 7. Coded character states for characters 181 210 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 8 8 8 8 8 8 8 8 8 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 1 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 Unnamed Taxon ? 1 1 ? 0 0 0/1 0 0 1 0 0 0 0 0 0 0 ? ? 1 ? ? ? ? ? ? ? ? ? 1 Cerrejonisuchus improcerus ? 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 ? 1 1 ? ? ? ? ? ? ? ? ? 1
225 Table C 8. Coded character states for characters 211 234 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 Unnamed Taxon ? ? ? ? ? ? ? ? ? ? ? ? 0 ? ? 1 0 ? ? ? 1 ? ? ? Cerrejonisuchus improcerus ? ? ? ? 0 0 ? ? ? ? ? ? 0 ? ? 1 1 ? ? ? 1 ? ? ?
226 APPENDIX D COMPARISON OF UNNAMED TAXON TO DIAGNOSES OF OTHER DYROSAURIDS Utilizing only characters that are used in the formal diagnos e s of other species of Dyrosauridae, the new taxon differs from t hese taxa in the following characters: F rom al l species of Dyrosaurus in: (1) shorter and wider snout; (2) at least 13 fewer upper teeth; (3) occipital tuberosities that are much wider transversally; (4) interfenestral bar that is squareshaped in cross section; (5) dorsal osteoderms that are thick an d not ornamented. F rom all species of Rhabdognathus in: (1) much shorter snout; (2) squareshaped supratemporal fenestrae, not elongate ones; (3) thick lateral arches of supratemporal fenestrae; (4) wide interfenestral bar; (5) anteroposteriorly short occipital tuberosities. F rom Acherontisuchus guajiraensis in: (1) shorter snout; (2) at least 8 fewer teeth; (3) lateral margin of maxilla is not straight in dorsal view. F rom Cerrejonisuchus improcerus in: (1) shorter snout; (2) orbits laterally placed. F rom Atlantosuchus coupatezi in: (1) much shorter snout; (2) lateral margin of premaxilla laterally curved and differentiated from lateral margin of maxilla; (3) nasals that penetrate between the posterodorsal premaxillary processes; (4) nasals not forming a d orsal boss. F rom Chenanisuchus lateroculi in: (1) shorter snout; (2) nasals fully unfused in adults; (3) large occipital tuberosities; (4) uncompressed teeth with striations; (5) at least three fewer teeth anterior to the orbit. F rom Sokotosuchus ianwilsoni in: (1) nasal penetrating the premaxilla. F rom Congosaurus bequaerti in: (1) shorter snout; (2) a jugal that does not extend anteriorly as far as the prefrontal; (3) a prefrontal nasal suture of similar length as the lac r imalnasal suture; (4) at least 6 fewer maxillary teeth. F rom Congosaurus compressus in: (1) alveoli that are circular, not oval. F rom Phosphatosaurus gavialoides in: (1) shorter snout; (2) modestly undulating lateral margin of maxilla in dorsal view; (3) squamosal forming modest posterolateral prong. F rom Hyposaurus rogersii in: (1) un compressed teeth that are not recurved; (2) carinae which are not displaced lingually; (3) unfused nasals present at least in some adult individuals.
227 F rom Guarinisuchus munizi in: (1) much larger body size; (2) posterior margin of parietal transversally straight. F rom Arambourgisuchus khouribgaensis in: (1) at least 6 fewer upper teeth; (2) teeth that are blunt and not elongated; (3) wide interfenestral bar.
228 APPENDIX E MODERN SPECIMENS USED FOR GEOMETRIC MORPHOMETRIC ANALYSIS List of specimens used for geometric morphometric analysis. Extant crocodylian specimens used in the geometric morphometric analysis (n= 242). Institutional Abbreviations : AMNH American Museum of Natural History, Herpetological Colle ctions, New York, NY, USA; ICN, Herpetological Collections of the Universidad Nacional, Bogot, Colombia; UF H University of Florida, Florida Museum of Natural History, Herpetology, Gainesville, FL USA; UF VP, University of Florida, Florida Museum of Natural History, Vertebrate Paleontology, Gainesville, FL USA; USNM Smithsonian United States Natural History Museum, Washington D.C. USA.
229 Table E 1. Extant crocodylian specimen list arranged by taxon and collection. Taxon Collection Specimen # Alligator A. mississippiensis UF H 39618 A. mississippiensis UF H 22215 A. mississippiensis UF H 34788 A. mississippiensis UF H 34886 A. mississippiensis UF H 35156 A. mississippiensis UF H 37230 A. mississippiensis UF H 39106 A. mississippiensis UF H 42548 A. mississippiensis UF H 42872 A. mississippiensis UF H 43151 A. mississippiensis UF H 50125 A. mississippiensis UF H 61483 A. mississippiensis UF H 67824 A. mississippiensis UF H 84197 A. mississippiensis UF H 109038 A. mississippiensis UF H 10941 A. mississippiensis UF VP 147700 A. mississippiensis UF H 155467 A. mississippiensis UF H 158960 A. mississippiensis UF VP 177250 A. sinensis UF H 67829 A. sinensis UF H 105540 A. sinensis AMNH R 139672 A. sinensis AMNH R 139673 A. sinensis AMNH R 140775 A. sinensis AMNH R 23898 A. sinensis AMNH R 23899 A. sinensis AMNH R 23900 A. sinensis AMNH R 23901 A. sinensis AMNH R 23907 Caiman C. crocodilus UF H 19067 C. crocodilus UF H 39062 C. crocodilus UF H 45439 C. crocodilus UF H 80910 C. crocodilus UF H 80911 C. crocodilus UF H 80912 C. crocodilus UF H 80913 C. crocodilus UF H 80914 C. crocodilus UF H 80915 C. crocodilus UF H 80916 C. crocodilus UF H 80917 C. crocodilus UF H 80918
230 Table E 1. Continued. Taxon Collection Specimen # C. crocodilus UF H 80919 C. crocodilus UF H 80920 C. crocodilus UF H 80921 C. crocodilus UF H 80922 C. crocodilus UF H 80923 C. crocodilus UF H 80924 C. crocodilus UF H 80925 C. crocodilus UF H 80926 C. crocodilus UF H 80927 C. crocodilus UF H 80 928 C. crocodilus UF H 80929 C. crocodilus UF H 80930 C. crocodilus UF H 80931 C. crocodilus UF H 80932 C. crocodilus UF H 80933 C. crocodilus UF H 80934 C. crocodilus UF H 80935 C. crocodilus UF H 80936 C. crocodilus UF H 80937 C. crocodilus UF H 80938 C. crocodilus UF H 80939 C. crocodilus UF H 80940 C. crocodilus UF H 80941 C. crocodilus UF H 80942 C. crocodilus UF H 80944 C. crocodilus UF H 80945 C. crocodilus UF H 80946 C. crocodilus UF H 80947 C. crocodilus UF H 80948 C. crocodilus UF H 80949 C. crocodilus UF H 80950 C. crocodilus UF H 80951 C. crocodilus UF H 80952 C. crocodilus UF H 80953 C. crocodilus UF H 80954 C. crocodilus UF H 80958 C. crocodilus UF H 80959 C. crocodilus UF H 99067 C. crocodilus UF H 154567 C. latir ostris UF H 62649 C. latirostris AMNH R 14183 C. yacare UF H 121231 C. yacare UF H 121249 C. yacare AMNH R 73622
231 Table E 1. Continued. Taxon Collection Specimen # C. yacare AMNH R 97298 C. yacare AMNH R 97299 C. yacare AMNH R 97300 C. yacare AMNH R 97303 C. yacare AMNH R 97304 C. yacare AMNH R 97307 C. yacare AMNH R 97308 C. yacare AMNH R 97309 C. yacare AMNH R 97329 C. yacare AMNH R 97330 Melanosuchus M. niger UF H 53600 M. niger UF H 62641 M. niger UF H 72914 M. niger AMNH R 58130 M niger AMNH R 58134 M. niger AMNH R 101419 M. niger AMNH R 110179 M. niger AMNH R 15171 M. niger AMNH R 58132 M. niger AMNH R 71172 M. niger AMNH R 97325 Paleosuchus P. palpebrosus UF H 62509 P. palpebrosus UF H 75020 P. palpebrosus UF H 75023 P. palpebrosus UF H 87980 P. palpebrosus AMNH R 137161 P. palpebrosus AMNH R 137162 P. palpebrosus AMNH R 137170 P. palpebrosus AMNH R 147051 P. palpebrosus AMNH R 93812 P. palpebrosus AMNH R 97327 P. palpebrosus AMNH R 97328 P. trigonatus UF H 6 1981 P. trigonatus AMNH R 129259 P. trigonatus AMNH R 129260 P. trigonatus AMNH R 137174 P. trigonatus AMNH R 66391 Crocodylus C. acutus ICN 1850 C. acutus UF H 49953 C. acutus UF H 54201 C. acutus UF H 56429
232 Table E 1. Continued. Taxon Collect ion Specimen # C. acutus UF H 63929 C. acutus UF H 115691 C. acutus UF H 151167 C. acutus UF H 151168 C. acutus UF H 157139 C. intermedius ICN 1849 C. intermedius ICN 1851 C. intermedius AMNH R 08790 C. johnstoni USNM 299810 C. johnstoni AMNH R 8 6540 C. mindorensis USNM 228407 C. moreletii UF H 29160 C. moreletii AMNH R 155461 C. niloticus UF H 54812 C. niloticus UF H 55787 C. niloticus UF H 154251 C. niloticus AMNH R 10081 C. niloticus AMNH R 23463 C. niloticus AMNH R 23464 C. niloticus AMNH R 23465 C. niloticus AMNH R 23466 C. niloticus AMNH R 7134 C. niloticus AMNH R 7136 C. niloticus AMNH R 118718 C. niloticus AMNH R 127255 C. niloticus AMNH R 137163 C. niloticus AMNH R 137180 C. niloticus AMNH R 137239 C. niloticus AMNH R 23 468 C. niloticus AMNH R 23469 C. niloticus AMNH R 71191 C. niloticus AMNH R 71192 C. niloticus AMNH R 73047 C. niloticus AMNH R 07852 C. niloticus AMNH R 23471 C. niloticus AMNH R 24717 C. niloticus AMNH R 29291 C. niloticus AMNH R 29292 C. novag uinae UF H 145927 C. novaguinae UF H 149214 C. novaguinae AMNH R 64425 C. palustris AMNH R 77632 C. palustris AMNH R 96134 C. porosus UF H 71779
233 Table E 1. Continued. Taxon Collection Specimen # C. porosus UF H 134586 C. porosus AMNH R 32338 C. po rosus AMNH R 62632 C. porosus AMNH R 62633 C. porosus AMNH R 66383 C. porosus AMNH R 66639 C. porosus AMNH R 66640 C. porosus AMNH R 66644 C. porosus AMNH R 76853 C. porosus AMNH R 24958 C. porosus AMNH R 58016 C. porosus AMNH R 74958 C. porosus AMNH R 15179 C. porosus AMNH R 24957 C. porosus AMNH R 74957 C. porosus AMNH R 06581 C. porosus AMNH R 07859 C. porosus AMNH R 29298 C. porosus AMNH R 07131 C. porosus AMNH R 29949 C. porosus AMNH R 58015 C. porosus AMNH R 69125 C. raninus AMNH R 29294 C. rhombifer UF VP 225401 C. rhombifer AMNH R 141073 C. rhombifer AMNH R 154087 C. rhombifer AMNH R 57773 C. rhombifer AMNH R 75033 C. rhombifer AMNH R 77595 C. siamensis AMNH R 118712 C. siamensis AMNH R 147950 C. siamensis AMNH R 49231 C siamensis AMNH R 72640 Mecistops M. cataphractus UF H 109154 M. cataphractus UF H 145926 M. cataphractus AMNH R 10074 M. cataphractus AMNH R 10075 M. cataphractus AMNH R 107634 M. cataphractus AMNH R 160902 M. cataphractus AMNH R 29300 M. cata phractus AMNH R 57772 M. cataphractus AMNH R 75424
234 Table E 1. Continued. Taxon Collection Specimen # Osteolaemus O. tetraspis UF H 33749 O. tetraspis AMNH R 10082* O. tetraspis AMNH R 10083 O. tetraspis AMNH R 101417 O. tetraspis AMNH R 101418 O. tetraspis AMNH R 117801 O. tetraspis AMNH R 117802 O. tetraspis AMNH R 160900 O. tetraspis AMNH R 160901 O. tetraspis AMNH R 24740 O. tetraspis AMNH R 29889 O. tetraspis AMNH R 69057 O. tetraspis AMNH R 75420 O. tetraspis AMNH R 75421 O. tetra spis AMNH R 7743 Tomistoma T. schlegelii UF H 54210 T. schlegelii UF H 62020 T. schlegelii UF H 84888 T. schlegelii UF H 107493 T. schlegelii USNM 52972 T. schlegelii AMNH R 113078 T. schlegelii AMNH R 15177 Gavialis G. gangeticus UF H 70592 G. gangeticus USNM 72562 G. gangeticus AMNH R 110145 G. gangeticus AMNH R 131377 G. gangeticus AMNH R 88316 G. gangeticus AMNH R 15176 G. gangeticus AMNH R 7138
235 APPENDIX F DYROSAURID FIGURES USED FOR GEOMETRIC MORPHOMETRIC ANALYSIS Dyrosaurid illustrations used for the geometric morphometric analysis. For Cerrejonisuchus improcerus a new reconstruction was made for this analysis based on the holotype, UF/IGM 29, and the referred specimen UF/IGM 31 (Fig. 51). A reconstruction was also made for Unnamed Taxon based on UF/IGM 67 69 (Fig. 5 1).
236 Table F 1. Reference images for Dyrosauridae. Taxon Reference Figure Cerrejonisuchus improcerus This study Fig. 5 1 Unnamed Taxon This study Fig. 5 1 Arambourgisuchus khouribgaensis Jouve et al., 2005b Fig. 4(A), p. 585 Atlantosuchus coupatezi Jouve et al., 2008 Text Fig. 4, p. 283 Chenanisuchus lateroculi Jouve et al., 2005a Text Fig. 5, p. 363 Dyrosaurus maghribensis Jouve et al., 2006 Fig. 5, p. 608 Dyrosaurus phosphaticus Jouve, 2005 Fig. 3, p. 327 G uarinisuchus munizi Barbosa et al., 2008 Fig. 2(b), p. 1387 Phosphatosaurus gavialoides Buffetaut, 1978 Fig. 2, p. 245 Rhabdognathus keiniensis Jouve, 2007 Fig. 8(1), p. 170
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250 BIOGRAPHICAL SKETCH Alex Hastings was born in Vermont, where he attended school until starting eleventh grade in Avon Lake, Ohio where he completed his high school degree. Following this, Alex attended Penn State University and obtained his B achelor of Science degree in Geosciences. While at Penn State he completed an undergraduate thesis under the direction of Dr. Roger Cuffey on fossil corals and br y ozoans of central Pennsylvania. In addition to his research on fossil crocodiles from Colombi a, he has also worked with fossil crocodylians of Panama and the Bahamas and fossil lungfish from Colombia. Alex is currently pursuing a career in paleontology and hopes to become a professor or curator in the field.